DA synthesised from tyrosine → L-DOPA → dopamine

Rate limiting step is tyrosine hydroxylase

Reuptake via DAT

Enzymatic breakdown via MAO and COMT

precurser is glutamine

Rate limiting step is glutaminase

Reuptake occurs via SERT

Enzymatic breakdown via MAO

precursor Glutamine

glutaminase

Reuptake into terminals via excitatory amino acid transporters (EAATs)

Taken up by glial cells and is converted into glutamine → glutamine is then transported out of the glial cells and into nerve terminals (glutamate-glutamine cycle)

precurser is glutamate

Rate limiting step is GAD

Reuptake via GAT-1

Enzymatic breakdown by gamma-aminobutyric acid transaminase (GABA-T)

μ receptors

κ receptors

δ receptos

NOP (ORL1 receptors)

Role

Synthesised from hydrolysis of ATP

Acts on GPCRs:

Role

Acts via:

Directly activated second messenger guanylate cyclase to produced cGMP

Major neurotransmitter in the CNS acting at GPCRs:

excitatory

Acts on a large number of receptors all of which are GPCRs (except 5-HT3 = ligand-gated ion channel):

Glutamate acts on two receptors:

Main excitatory neurotransmitter in the CNS and is found in all regions of the CNS

GABA acts via two receptor subtypes:

It is an inhibitory CNS neurotransmitter, along with glycine

inhibitory

• 4 subtypes of opioid receptor (all GPCRs)

receptor subtypes

functional type

synaptic responses they mediate

receptor subtypes

functional type

synaptic responses they mediate

Does not act at a receptor:

mediator in the PNS/CNS

Reward, desire, emotion

Cognition, motivation, emotion

Movement

Prolactin secretion

Stimulates secretion of watery saliva

Stimulates secretion of thick, viscous saliva

α1, β2

Stimulates sphincter pupillae muscles; constricts pupils

Stimulates dilator pupillary muscles; dilates pupils

α1

PNS

SNS

Sympathetic Receptor

PNS

SNS

Little or no effect

Constricts most vessels and ↑ BP; constricts vessels of abdominal viscera and skin to divert blood to muscles, heart, and brain when necessary; adrenaline weakly dilates vessels of skeletal muscles during exercise

α1

Constricts bronchioles

Dilates bronchioles

β2

↑s motility and amount of secretion by digestive organs; relaxes sphincter to allow foodstuffs to move through tract

Decreases activity of glands and muscles of digestive system; constricts sphincters

α1, β2

No effect

Stimulates medulla cells to secrete adrenaline and noradrenaline

Nicotinic

No effect

Stimulates copious sweating (cholinergic fibers)

Muscarinic

PNS

SNS

PNS

SNS

the amount of neurotransmitter released and

the time neurotransmitter stays in the area

excitatory (depolarisation – usually Na+ entry)

↓ with distance

If strong enough (many EPSPs) → reach threshold at trigger zone

inhibitory (hyperpolarisation – usually Cl- entry or K efflux)

↑ -ve potential

Makes membrane more negetive

LGIC

GPCR

↓ cAMP -> ↓ activity of voltage-gated Ca2+ channels -> ↓ neurotransmitter release

Regulate balance, posture, and eye movements.

Receives input from the vestibular system, which senses changes in head position and movement, and integrates this information to control equilibrium and coordination of eye movements.

It receives sensory input from the spinal cord regarding proprioception, muscle tone, and touch.

Coordinating and refining voluntary movements, muscle synergy, and maintaining muscle tone.

Ensure smooth and accurate execution of motor activities and coordination of posture.

It receives input from motor cortex, involved in motor planning, coordination, and fine motor control.

contributes to the timing, precision, and coordination of movements, including skilled and voluntary movements of the limbs, speech articulation, and cognitive processes related to motor tasks.

at the base of each hemisphere

egg-shaped and centrally located on either side of the 3rd ventricle

Above the midbrain, below the corpus callosum, between the cerebral hemispheres.

bounded by the fornix superiorly

medially, the thalami are connected by grey matter (interthalamic adhesion)

the posterior limb of the internal capsule (white matter) fibres is the lateral limit

more on the functions of thalamus in week 6 (focus on know there are 5 nuclei, but reletively LY) (just know that the thalamus is a major relay station and focus on week 6)

anterior nucleus?

medial nuclei?

ventral nuclei?

lateral nuclei?

posterior nuclei?

forms the floor of the 3rd ventricle and extends from the area superior to the optic chiasm anteriorly, to the mamillary bodies posteriorly

posterior to the optic chiasm, the infundibulum (pituitary stalk) extends inferiorly, connecting the hypothalamus to the pituitary gland

controls and integrates the function of the ANS and the endocrine system

dorsomedial to the thalamus and next to the roof of the 3rd ventricle

habenular nucleus = ANS function such as emotional and visceral responses to odours

pineal gland = influences pituitary function and produces melatonin to maintain seasonal and circadian rhythms

inferior to the thalamus

between the thalamus and tegmentum (roof) of the midbrain

Functionally part of the basal ganglia

prominent gray matter nuclei involved in motor control.

responsible for sequencing of patterned movement

Regulating motor output and contributing to the control of voluntary movements, including initiating and inhibiting specific motor patterns.

2023 SA exam asked to lable peduncles

Fiber tracts that connect the cerebrum with the rest of CNS

Carry motor info from cerebral cortex to spinal cord and other parts of the body.

Superior colliculi are involved in visual processing and contribute to the coordination of eye movements and visual reflexes.

Inferior colliculi role in auditory processing and relay auditory information to the thalamus.

Dysfunction associated with Parkinson's.

dopamine-producing nucleus involved in motor control, reward, and movement coordination.

Functionally is part of the basal ganglia.

CN nuclei V to VIII

4th ventricle lies posterior, between pons and cerebellum

It acts as a bridge between different brain regions, connecting the cerebrum and cerebellum via the superior, middle and inferior cerebellar peduncles.

Respiratory centers

lie on the anterior aspect within the pyramids.

90% of fibres cross the midline at the decussation of the pyramids.

The cardiac center

Respiratory center

Vasomotor center

Ventrolateral portion of the medulla and contains the inferior olivary nucleus.

Feedback to the cerebellum fand part of an involuntary motor pathway.

Posterior aspect of the medulla and involved in processing of sensory information.

Both nuclei receive primary sensory information from the fasciculus gracilis (lower limbs) and fasciculus cuneatus (upper limbs), respectively.

Serve as relay stations, where the first order neurons synapse with second-order neurons.

involved in emotional processing, attentional control, and decision-making.

Role in regulating emotional responses and monitoring errors in behavior.

important role in memory

Processing and regulation of emotions, particularly fear and aggression.

Role in the formation of emotional memories and the recognition of facial expressions.

Regulates numerous physiological processes, including temperature control, hunger, thirst, sleep and sexual appetite.

Regulation of the ANS and release of hormones from the pituitary gland.

Mammillary bodies, located in the hypothalamus, are involved in memory formation and retrieval.

White matter tract that connect the hypothalamic and hippocampus systems. serves as a major pathway for communication between various limbic structure

Transmission of signals related to memory and emotional processing.

Formation and retrieval of new declarative memories, which include facts and events.

Contributes to spatial navigation and consolidation of memories from short-term to long-term storage.

arcuate fasciculus, which connects Broca's area and Wernicke's area, is a prominent example, aiding in language processing.

corpus callosum is the largest commissural fiber, linking the two cerebral hemispheres and enabling them to share information.

internal capsule is a major projection fiber that carries motor signals from the cerebral cortex to the brainstem and spinal cord and sensory signals back to the cortex.

Responsible for sensory integration

Primary motor cortex – motor control

Premotor and supplementary motor – motor planning

Broca’s – motor planning for speech

During neurulation, neural crest cells form at the edges of the neural folds .

As the neural tube closes and separates from the ectoderm, these neural crest cells first joint from both sides, divide and begin to migrate to various parts of the embryo.

Differentiate into diverse cell types, including neurons, glial cells, and components of the PNS.

Begins around day 22 of embryonic development, starting at the midline and proceeding both proximally (towards the head) and distally (towards the tail).

Proximal part closes by ~ day 25

Distal part closes by ~ day 27.

Disturbance of neurulation results in brain and spinal cord abnormalities by:

when neural tube fails to close correctly, leaving nervous tissue vulnerable to external factors, results in significant abnormalities to brain and spinal cord.

Spina Bifida

Anencephaly

left MCA

embolic stroke

thrombotic stroke

Occlusion of the MCA

RADIOLOGY MSAT HY

Subarachnoid

Intracerebral

Cerebellar

Extradural

Subdural

CSF overproduction

obstructed CSF flow

decreased absorption of CSF

complications in adults vs infants?

0-15mm Hg

Pressure on parts of the brain – neuronal injury

Blood supply may be compromised to rest of the brain

BBB may be bypassed by a haemorrhage

o Provides protection

o Prevents lateral displacement of the brain

 Downward projection

 Extends between the cerebral hemispheres

 Horizontal projection

 Extends between the occipital lobes of the hemispheres and the cerebellum

 Small midline projection in the posterior cranial fossa

 Its anterior edge is free and is between the two cerebellar hemispheres

 Small horizontal shelf

 Covers the hypophysial fossa in the sella turcica of the sphenoid bone

 There is an opening in the centre through which the infundibulum passes, connecting the pituitary gland with the base of the brain, and any accompanying blood vessels

aorta

Bifurcate into Internal and External Carotid Arteries

Where does it bifurcate?

passes superiorly in the neck to the base of the skull

enters the carotid canal

passes within the petrous part of the temporal bone anteromedially

ophthalmic artery

anterior cerebral artery (ACA)

middle cerebral artery (MCA)

posterior communicating artery

supratrochlear and supraorbital arteries from the internal carotid artery

Superior thyroid artery

Ascending pharyngeal artery

Lingual artery

Facial artery

Occipital artery

Posterior auricular artery

Maxillary artery

Superficial temporal artery

Some Anatomists Like Freaking Out Poor Medical Students

Equalise vascular supply

Alternate flow if blocked (lessening affect of stroke)

leision of PCA would affect the occipital lobe and mainifest in symptoms such as visual disturbance, and visual recognition loss (2023 exam Q)

originates at the terminal bifurcation of the basilar artery (BA).

Runs along the inferior brain surface to supply anterior and inferior temporal lone and inferior and medial ocipital lobe

lateral branch of the posterior cerebral artery

Arise from subclavian arteries

Travel through transverse foramina

Through foramen magnum

Unite to form the Basilar Artery over surface of the pons

Two terminal branches - Posterior cerebral arteries

Remove waste products and metabolic byproducts from neural tissue.

Carry essential nutrients, ions, and metabolic products to the neural tissue.

Act as a cushion, absorbing and distributing mechanical forces that could potentially damage the neural tissues.

Regulates ICP

Regulate temperature by dissipating heat and maintaining stable thermal environment.

Allow the brain to float within the skull, preventing crushing of CNs and blood vessels.

Muscle mass receiving innervation from the fibres conveyed by a single spinal nerve

Specific muscle groups innervated by motor fibres from a single spinal nerve root. They can be used to assess and localize spinal cord injuries by evaluating muscle strength and motor function.

By testing muscle strength in specific myotomes, clinicians can identify areas of weakness or paralysis.

Area of skin innervated by cutaneous branches of a single SN

Dermatomes exist for each of these spinal nerves, except for C1.

Dermatomes overlap, so lesion of one spinal nerve is of little consequence

A lesion of a single spinal nerve would not results in numbness over that area normally supplied by that nerve. At least 2 adjacent nerves must be interrupted to produce discernible area of numbness.

lesion along the sympathetic pathway due to stroke, tumor, spinal cord injury or aneurysm of the carotid artery

ptosis

decrease pupil size

reduced pupillary reflex

anhidrosis (on the affected side of the face)

red conjunctivae

Found only in the thoracic and lumbar regions between T1 to L2.

Cell bodies always in lateral horn of T1 to L2

Sympathetic chain runs along the spinal column on both sides, connecting to SN

Organised somatotopically (head is most superior, pelvis is most inferior).

Supply blood vessels, arrector pili muscles, sweat glands & viscera

Pathways

As soon as presynaptic enters the anterior primary rami, they leave via white rami communicantes to sympathetic trunk. One of the following occurs:

Sympathetic to Suprarenal Gland

Splanchnic Nerves

Paravertebral ganglia and the nerve fibres that travel between them form the sympathetic chains.

Prevertebral ganglia form plexuses that surround the unpaired visceral branches of the aorta (celiac, superior mesenteric, inferior mesenteric AND aorticorenal)

The pupils of the eyes dilate

HR force of heart contraction and BP ↑

airways dilate allowing faster movement of air into and out of the lungs

blood vessels that supply the kidneys and GIT constrict, decreasing BF, resulting in reduced urine formation and digestive activities

Blood vessels of skeletal muscles, cardiac muscles, liver and adipose tissues dilate, allowing greater BF

Liver cells perform glycogenolysis to ↑ glucose in the bloodstream and lipolysis

Peristalsis of GIT and digestive secretions slow down/stop

originates from the craniosacral regions (brainstem [CNs III, VII, IX, X] and sacral spinal cord [S2-S4]), with long preganglionic and short postganglionic fibers.

Presynaptic parasympathetic neuron cell bodies are in the brainstem and leave through CNs III, VII, IX and X. Each has a visceral motor ganglion

Presynaptic neuron cell bodies are in the brainstem.

This constitutes the cranial outflow.

These fibres leave through cranial nerves III, VII, IX and X.

In the head, there are 4 ganglia:

S2 to S4 cell bodies in lateral horn of spinal cord

Leave through S2 to S4 spinal nerves – pelvic splanchnic

Supplies hindgut, bladder and genitalia

Preganglionic neurons ihave their cell bodies in the brainstem or sacral spinal cord.

Preganglionic fibers are generally long and travel to ganglia that are located very close to or within the walls of the target organs.

The postganglionic neurons are typically short because they are near or within the target tissue.

This division enhances rest and digest activities that support body functions that conserve and restore body energy during times of rest and recovery

Impulses to the digestive glands and the smooth muscles of the gastrointestinal track allows food to be digested and absorbed

There is a reduction in body functions that support physical activity.

Preganglionic fibers: Short, as they synapse close to the spinal cord in the sympathetic chain or prevertebral ganglia.

Postganglionic fibers: Long, as they extend from the ganglia to the target organs.

Preganglionic fibers: Long, as they travel to ganglia near or within the target organs.

Postganglionic fibers: Short, because they are close to or within the target organs.

transmit sensory information from the body’s receptors to CNS

Includes sensations like pain, temperature, touch, and proprioception

Somatic afferents

Peripheral Distribution of SN

transmit motor commands from CNS to muscles and glands

Motor pathways

consists of afferent fibres and their cell bodies lie in the dorsal root ganglion.

Extend peripherally to a sensory receptor and centrally to the dorsal horn of the spinal cord gray matter.

consists of efferent fibres passing from nerve cell bodies in the anterior horn of the spinal cord to effector organs

It immediately divides into two rami: anterior and posterior primary rami. These and all of their branches are mixed nerves, containing both sensory and motor information.

Dorsal column (top)

Spinothalamic (bottom)

These are both taken to the thalamus, and then to the cerebrum so we are consciously aware of these sensations.

Spinocerebellar (middle)

volentary motor pathways

involuntary motor pathways

Carry preganglionic fibres from spinal cord to paravertebral or prevertebral ganglia

Communicantes exist only at the levels where lateral horn is (T1-L2).

Carry postganglionic fibres from paravertebral or prevertrebral ganglia to target organ

Communicantes exist at EVERY LEVEL OF THE SPINAL CORD.

Postganglionic neurons from paravertebral ganglia to their destination and carrying those preganglionic nerve fibres which enter the paravertebral ganglia but do not synapse.

Ptosis

Affected eyeball deviates down and laterally

Inability to accommodate causes blurred vision

Pupillary dilatation causes glare

GLS: Give the name of the cranial nerve that is most responsible for conveying somatosensation from the head and neck and detail the branches/divisions of this nerve plus the area/structures supplied:

Mesencephalic Nucleus:

Main/Chief/Principal Sensory Nucleus:

Spinal Trigeminal Nucleus:

the cochlear nerve, which transmits sound information from the cochlea to the brain.

the vestibular nerve, which carries information about balance and head position from the vestibular apparatus.

Both branches carry SSA, which pass through internal acoustic meatus into the petrous part of the temporal bone where they innervate the cochlea and semicircular canals.

General somatic afferent – cutaneous sensation from external ear and posterior 1/3 of tongue

General visceral afferent – visceral sensations from parotid gland, carotid body, pharynx and middle ear

Special visceral afferent – taste sensation from posterior 1/3 of tongue

Special visceral efferent – (NOT GSE because it’s not from somites) is branchial, provide motor to stylopharyngeus muscle, which assists with swallowing

asking the patient to protrude their tongue

Damage to the hypoglossal nerve causes paralysis of the tongue

S – sensory

M – motor

B – both

V, VII, IX and X (somatosensation)

I, II, VII, VIII, IX, X (special senses)

III, IV, VI, XI, XII (somatic)

V, VII, IX, X (branchial)

III, VII, IX, X (visceral/parasympathetic)

CN III, which supplies the ciliary muscles of the eye for lens accommodation and pupillary constriction (sphincter pupillae)

CN VII, which innervates the lacrimal gland, submandibular, and sublingual glands for tear and saliva production.

CN IX stimulates the parotid gland for salivation

CN X provides extensive parasympathetic innervation to thoracic and abdominal viscera, regulating heart rate, digestive functions, and respiratory rhythm.

General Somatic Afferent (GSA): From somatic structures. Carry sensory information such as touch, pain, and temperature from the skin and mucous membranes.

General Visceral Afferent (GVA): From visceral structures. Transmit sensory signals from the internal organs, like the heart and digestive tract, including sensations such as distension and discomfort.

Special Visceral Afferent (SVA): Special sensation. convey information related to special senses, namely taste and smell.

Special Somatic Afferent (SSA): Special sensation. convey information related to special senses, including vision, hearing, and balance.

Voluntary (skeletal) muscles

Involuntary muscles (GVE)

These nuclei are responsible for generating the motor output that controls various muscles in the head and neck.

Somatic motor nuclei

Visceral motor nuclei

ciliary ganglion

pterygopalatine ganglion

submandibular ganglion

otic ganglion

CN III – Oculomotor

CN VII – Facial

CN IX – Glossopharyngeal

CN X – Vagus

CN IX – Glossopharyngeal (GSA, GVA, SA)

CN X – Vagus (GSA, GVA, SA)

Cranial Root

Spinal Root

these ascend and enter the skull through the foramen magnum and it exits the skull through the jugular foramen.

After exiting the cranium via the jugular foramen, the cranial and spinal roots typically separate.

Spinal Part: Descends along the internal jugular vein, passing deep to the sternocleidomastoid muscle and then innervates it. It continues across the posterior triangle of the neck to the trapezius muscle, which it also innervates.

Cranial Part: combines with the vagus nerve to contribute to innervating muscles of the pharynx, larynx, and soft palate.

Spinal Part:

Cranial Part:

GSA – carry sensation from auricle, external acoustic meatus and dura mater of posterior cranial fossa

GVA – visceral sensations from pharynx, larynx, trachea, bronchi, heart, oesophagus, stomach and intestines, up to the left colic flexure

SVA – special sensation of taste from epiglottis and palate

SVE – branchial, provide motor to muscles of the pharynx (except stylopharyngeus), larynx, palate (except tensor veli palatini) and superior 2/3 of oesophagus

GVE – parasympathetic innervation to the smooth muscles and glands of the trachea, bronchi, coronary arteries and the gastrointestinal tract. It supplies the pulmonary, cardiac and oesophageal plexuses in the thorax and descends into the abdomen to supply parasympathetic innervation to the foregut and midgut.

Arises from the medulla

Exits the cranium via the jugular foramen.

Descends in the neck within the carotid sheath, alongside the internal jugular vein and common carotid artery.

Travels down into the thorax, giving off branches like the recurrent laryngeal nerve (which loops under the aorta on the left and the subclavian artery on the right) before continuing into the abdomen.

is a mixed nerve with the widest distribution, supplying the thoracic organs, foregut and midgut with parasympathetic innervation.

Cervical Region: Supplies branches to the pharynx, larynx (including the recurrent laryngeal nerve), and soft palate. The superior laryngeal nerve (branch of the vagus) also supplies the cricothyroid muscle and provides sensory innervation above the vocal cords.

Thoracic Region: : Provides parasympathetic innervation to the heart (cardiac branches) and lungs (pulmonary branches), regulating heart rate and bronchoconstriction.

Abdominal Region: Extends into the abdomen, providing parasympathetic innervation to the majority of the gastrointestinal tract up to the splenic flexure, including the stomach, liver, pancreas, kidneys, and intestines.

arises from the anterior rami of the cervical spinal nerves C3, C4, and C5, with C4 being the primary contributor ("C3, 4, and 5 keep the diaphragm alive").

Descends along the anterior scalene muscle in the neck, passing posterior to the subclavian vein and anterior to the subclavian artery.

Enters the thorax by passing between the subclavian artery and vein.

In the thorax, the phrenic nerve descends anteriorly to the root of the lung, passing along the pericardium of the heart.

Motor Innervation: primarily innervates the diaphragm

Sensory Innervation: central part of the diaphragm, the pericardium, and parts of the pleura and peritoneum (lining the thoracic and abdominal cavities, respectively).

GSA – general sensation to ear

SVA – taste from the anterior 2/3 of tongue

GVE – Parasympathetic to lacrimal, submandibular & sublingual glands

SVE - parotid gland where it divides into 5 terminal branches: supplies the muscles of facial expression. Branchial motor to muscles of facial expression

Facial nerve branch called the chorda tympani hitchhikes onto the lingual nerve to get into the oral cavity

Does not originate in the brainstem; fibers arise from the olfactory epithelium.

SVA

Does not originate in the brainstem; fibers arise from the retina.

SSA

Midbrain (oculomotor nucleus and Edinger-Westphal nucleus).

- GSE

- GVE

Midbrain (trochlear nucleus).

GSE

Pons (trigeminal motor nucleus and sensory nuclei).

- GSA

- SVE

Pons (abducens nucleus).

GSE

Pons (facial nucleus, superior salivatory nucleus).

GSA

SVA

SVE

GVE

Pons/Medulla junction (vestibular and cochlear nuclei).

SSA

Medulla (nucleus ambiguus, inferior salivatory nucleus).

GSA

GVA

SVA

SVE

GVE

Medulla (nucleus ambiguus, dorsal motor nucleus of the vagus).

GSA

GVA

SVA

SVE

GVE

Medulla (nucleus ambiguus) and spinal cord (spinal accessory nucleus in the cervical region).

GSE

Medulla (hypoglossal nucleus).

GSE

Naked nerve endings

Pain and temperature receptor

Elaborate structures around nerve endings

Pressure, vibration and stretch

Sensory receptors in the muscles, joints, tendons and skin

Protect the muscle and provide a sense of the position of the muscle

Most structurally and functionally complex of general sensory receptors

Complex receptors – lie parallel with the fibers - located in the muscle belly

Senses length and rate of change in length

Detects both static and dynamic changes in muscle length

Consist of intrafusal muscle fibers in parallel with extrafusal muscle fibers

Intrafusal fibers: sensory components of muscle spindles

When the muscle stretches (↑ length) → stretches muscle spindle → stimulates both Type Ia and Type II sensory afferents

Muscle Spindles

Area 2 of S1 is specifically responsible for processing complex tactile information, including the integration of sensory inputs related to object size, shape, and spatial aspects.

Also called primary somatosensory area.

Inputs from thalamus and is more extensive in processing sensory information

Processes basic touch info, including location, texture, and shape.

S1 comprises four sub-areas (1, 2, 3a, and 3b)

Sensory Homunculus

contribute to localization, learning, and memory processes

involved in higher-level functions, such as recognizing object size and texture and integrating bilateral sensory inputs.

Located behind S1 → integrate sensory inputs → form comprehensive understanding of stimuli.

Areas 5 and 7, located behind S1

Deciphers the meaning of stimuli

Allows for the perception of size, texture, and the relationship between parts

Cortical circuits can reorganize in response to differential stimulation or training, which ↑s sensory input

Sensory info from the somatic segments to the spinal cord through the dorsal roots of the spinal nerves

Spinal cord to the brain by ascending pathways

Directly to brain stem via cranial nerves

The dorsal column system/dorsal column–medial lemniscal system

The anterolateral system

Primary afferent neurons have their cell bodies in dorsal root or cranial ganglia, and their axons synapse on somatosensory receptor cells

Axons of 2nd-order neurons cross midline, either in the spinal cord (anterolateral system) or in the brain stem (dorsal column system)

Decussation means that somatosensory information from one side of the body is received in the contralateral thalamus

Thalamus has a somatotopic arrangement of somatosensory information

Touch sensations requiring a ↑ degree of localization and transmission of fine gradations of intensity

Vibratory sensations

Sensations that signal movement against the skin

Position sensations from the joints

Pressure sensations related to fine degrees of the judgment of pressure intensity

Anterior – Pressure, crude touch

Lateral – Pain, temperature

Principal sensory trigeminal nucleus – Fibers carrying tactile impulses

Spinal nucleus – Fibers carrying pain and temperature

Mesencephalic nucleus – Fibers carrying proprioceptive impulses

Receptors – Muscle spindle and Golgi tendon organs

Tract - Terminates to the same side of the cerebellum (ipsilateral)

Function - Movement and position mechanisms

Dorsal spinocerebellar tract

Ventral spinocerebellar tract

Meissner’s corpuscles

Merkel cells

Ruffini corpuscles

Pacinian corpuscles

Other Classifications

Respond to noxious stimuli that can produce tissue damage

Thermal or mechanical nociceptors

Polymodal nociceptors

Free nerve endings – terminate in subcutaneous layers - Slowly adapting

Cold and warm receptors

Detect rapid changes in the stimulus

Detect onset and offset of a stimulus

Communicates the dynamic nature of the stimulus – when it begins and when it ends – to provide a sense of stimulus movement

Some tactile receptors

Detect steady pressure

Encode duration and intensity

Communicates the static nature of the stimulus (size, shape)

Pain, proprioception; some tactile receptors

Stimulus energy converted into information processed by CNS

Ion channels or second messengers initiate membrane potential change

Mediated through opening or closing specific ion channels

RP is a change in membrane potential of the sensory receptor

RP is graded

Non-propagated depolarizing potential

↑ stimulus strength → magnitude of the RP ↑

Magnitude of generator potential above 10 mV an AP is generated → nerve impulse

Produced in the unmyelinated nerve terminal

RP summate to threshold stimulus → initiates an AP

A single sensory axon and all of its peripheral branches

Area supplied by one sensory unit usually overlaps and interdigitates with the areas supplied by others

Spatial distribution from which a stimulus produces a response in that unit

Ability to distinguish two nearby objects touching the skin as two distinct points

It is the perception of the form and nature of an object without looking at it

Smaller receptive field → more precisely the sensation can be localized or identified

Considerable overlap with neighboring sensory afferents

1st-order sensory neurons have the simplest receptive fields

3rd-order sensory neurons have complex receptive fields

The first image

The second image in the bipolar cells

The third image in the ganglion cells

All fibers from nasal halves of retina cross to the opposite side and join fibers from the opposite temporal retina to form optic tract

Nerve fibers from each nasal hemiretina cross at the optic chiasm and fibers from each temporal hemiretina remain uncrossed

Axons from retinal ganglion cells form the optic nerves and optic tracts synapse in the thalamus

From LGN to primary visual cortex - optic radiation

Two principal functions of LGN

Magno and parvocellular layers in LGN

“M” ganglion cells of the retina neural network have large cell bodies, and their axons ascend to the magnocellular layer of the LGN

“P” ganglion cells of the retina have small cell bodies, and their axons ascend to the parvocellular layer of the LGN

Damage to the parvocellular layer decreases acuity and colour perception but not motion detection

Damage to the magnocellular layer decreases ability to perceive motion but not to analyse size, shape and colour of objects

LGN projects to primary visual cortex or striate cortex by way of the visual radiations

The primary visual cortex - Brodmann area 17 or V1

The visual cortex contains a retinotopic map

Representation of the macula occupies the most posterior and largest part of both gyri

Fovea has several hundred times as much representation in the primary visual cortex

Extrastriate Visual Cortex

Deficiency of Vitamin A – impaired dark adaptation – Night blindness

Moving from brightly lit area to a dimly lighted environment - the individual becomes “accustomed to the dark”

Retina becomes more sensitive to light - with increasing time spent in darkness

Decline in visual threshold - is known as dark adaptation (20 min)

Rods are responsible for the dark adaptation response

Dark adaptation time depends on the rate of regeneration of rhodopsin (depends on Vitamin A)

Moving from dim to a brightly lighted environment

Intense light – uncomfortably bright

In sustained bright light, a large proportion of rhodopsin will dissociate to retinal and opsin

Eyes becomes adapted to light by having less visual pigment available for phototransduction

Visual threshold ↑s – light adaptation (5 min)