neuroscience part 3

Autonomic nervous system

subdivision of the PNS

regulates body activities that are not under conscious control

visceral motor innervates non-skeletal muscles

ANS is composed of special group of neurons serving

cardiac muscle

smooth muscle

internal organs and skin

ANS motor neurons

preganglionic (in brain or spinal cord) then to ganglionic (cell body in ganglion outside CNS)

difference between SNS and ANS

somatic neuron goes straight to skeletal muscle

autonomic has preganglionic and post ganglionic fibres going to to smooth muscle glands and cardiac muscle

divisions of ANS

parasympathetic and sympathetic

parasympathetic

routine maintenance rest and digest

craniosacral

only innervate internal organs

cholinergic (acetylcholine)

sympathetic

mobilization and increased metabolism

thoracolumbar

lead to every part of the body

adrenergic post ganglion (noradrenaline)

(acetylcholine in preganglionic)

Central control of ANS

Amygdala

hypothalamus

reticular formation

Amygdala ANS

main limbic region for emotions

stimulates sympathetic activity

hypothalamus ANS

main integration centre

Reticular formation ANS

most direct influence over autonomic function

ANS diseases

horner’s syndrome

Raynauds disease

Horners syndrome

pupillary constriction

ptosis

loss of sweating

vasodilation

enophthalmos

Raynaud’s disease

hyperactivation of the sympathetic NS causing extreme vasoconstriction of peripheral blood vessels leading to hypoxia

corticospinal tract

carries movement information form motor cortex to spinal cord

upper motor neurons to lower motor neurons to muscle

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corticospinal tract structure

motor cortex to midbrain(cerebral peduncles) to pons and medulla (pyramids) cross to other side of brainstem (pyramidal decussation)

major vertebral regions

cervical

thoracic

lumbar

sacral

coccygeal

sensory dermatomes

area of skin supplied by sensory neurons that arise from spinal nerve ganglion

sensory input

comes though dorsal horn

motor output

comes through ventral horn

types of skeletal muscle fibres

slow oxidative (slow fatigue resistant)

fast oxidative (fast fatigue resistant)

fast glycolytic (fast fatiguing)

differences in maximal shortening velocities are due to…

myosin enzymes with high or low ATPase activities

Slow oxidative motor units

first during weak contractions

fast-glycolytic motor units

strong contractions

larger average diameter = greater tension but faster fatigue

large number of fibres per motor unit

Type 1 fibres

red

thin with large amounts of myoglobin and mitochondria

isoform of myosin with low ATPase activity

contraction slower an lower intensity

sustained production of force

type 2 fibres

white

thick and contain less myoglobin

isoform myosin with high ATPase activity

contraction fast

few mitochondria

short-lasting maximal contraction

rely on anaerobic glycolysis

muscle spindle

in fleshy part of muscle

detects rate of change at which the muscles fibres are stretched

changes in length of muscle fibres

aids in coordination and efficiency of muscle contraction

patellar reflex

patellar ligament is stretched pulling on patella which in turn stretches patellar tendon stretching quads causing muscle spindles to stretch

active muscles spindles excite associated neurons

olfaction

smell

olfactory receptor neurons on olfactory epithelium

olfactory receptor cells synapse with tufted cells and mitral cells becoming the lateral olfactory tract

gustation

taste

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G olf

G-protein coupled to the receptor cell for olfaction

olfaction pathway

2 pathways

1 to olfactory blub then to thalamus then to cortex

2 to uncus then lateral hypothalamus to cortex

tongue

supplied by cranial nerve

papillae 3 types of undulations on the tongue

Papillae

3 types of undulations on the tongue

circumvallate

foliate

fungiform

circumvallate

taste buds on sides

foliate

taste buds in middle

fungiform

taste buds on top

gustatory cell

specialized non neuronal cell

has cilia at the top

saliva

dissolves compounds to be brought onto the taste buds

cannot taste without it

salt taste receptor cell

enters through sodium channel and depolarizes cell - calcium influx - transmitter release - increased firing in afferent nerve(cannot be manipulated or adapted)

sour taste receptor cell

acidic, hydrogen ions (protons) enter and depolarizes cell - calcium influx - transmitter release - increase firing in afferent nerve

sweet taste receptor cell

binds to a receptor with g-protein activating cAMP depolarizing cell - calcium influx - transmitter released - increased firing of afferent nerve

umami taste receptor cell

g-protein coupled receptor

bitter taste receptor cell

g-protein coupled receptor

increasing IP3 causing calcium release and transmitter release and increasing afferent nerve firing

transmission of taste information

from taste buds to cerebral cortex via synapses in the brain stem and thalamus

middle ear bones

malleus

incus

stapes

cochlea structure

cochlear nerve

scala vestibuli

scala tympani

cochlear duct

==**organ of corti**==

organ of corti structure

hair cells

stereocilia

tectorial membrane

nerve fibres

blood vessels

basilar membrane

organ of corti mechanism

basilar membrane vibrates hair cells causing stereocilia to be pushed against tectorial membrane mechanically gated ion channels open up

endolymph

high potassium

potassium enters

depolarizes hair cell

perilymph

high sodium

basilar membrane responds to high frequency at…

base near oval window

basilar membrane responds to low frequency at…

apex further from oval window

auditory pathway

in through cochleo-vestibular nerve to brainstem, crosses over to superior olive to inferior colliculus to auditory cortex and thalamus

loudness

imp/s along the cochlear nerve

pitch

position along basilar membrane

sound location

interaural timing and intensity differences

vestibular system components

cochlea

saccule

ampulla utricle

3 semicircular canals and ducts

otolith organs

utricle and saccule (in gelatinous substance)

semicircular ducts function

detects angular acceleration during rotation of the head

otoliths function

move in response to changes in linear acceleration and the position of the head relative to gravity

vestibular hair cells

type 1 kinocilium

type 2 stereocilia

hair cells move to right

ion channels open

stimulation

depolarization

cells hairs move to the left

ion channels close

inhibition

hyperpolarization

connections of vestibular system

into spine through vestibular nerve goes to spinal cord to thalamus to cerebral cortex to eyes

vestibulo-ocular reflex

helps maintain fixation of eyes on an object with movement of the head

vestibulospinal reflex

allows for input from vestibular organs to be used for posture and stability in gravity environment

utricle responds to

linear acceleration in all directions

eye layers

fibrous outer

middle choroidal

inner neural

fibrous outer layer

cornea and sclera

continuous with dura mater

middle choroidal layer

vascular posteriorly

forms iris and ciliary body anteriorly

continuous with arachnoid and pia

inner neural layer

retina

continuous with CNS tissue

optic disc

where optic nerve exits retina

pale circular region

no photoreceptors (blind spot)

macula

circular region adjacent the optic disc

central vision

centre is a depression called the fovea

anterior chamber

space between cornea and iris

posterior chamber

space behind the iris containing the lens

vitreous chamber

space behind the lens

aqueous humour

substance in the anterior and posterior chamber

oxygenated directly from the atmosphere

the lens and cornea are…

avascular

refractive index

measure of how much the speed of light is reduced traveling through a given medium relative to a vacuum

Rf of lens of the eye

1\.45

refraction

takes place at both cornea and the lens

more refraction at cornea since it has air on one side

myopia

image falls short of retina

needs corrective concave lens

hyperopia

image overshoots retina

needs corrective convex lens

light through the eye

enters the cornea and projected on to back of eye and converted into electrical signals by photoreceptors in the retina

photoreceptors

sensory receptors responsible for vision

sensory receptors

neurons or epithelial cells that can transduce energy from stimulus into electrical signals called receptor potentials

receptor potentials

graded potentials that can either be depolarizing or hyperpolarizing

retinal neurons

2 classes of photoreceptors

3 classes of interneurons

types of photoreceptors

rods and cones

interneurons

connect photoreceptors to ganglion cells

bipolar, horizontal and amacrine

cones

day vision

loss of function = legally blind

high visual acuity, temporal resolution and mediate colour vision

rods

mediate night vision

loss of rods = night blindness

extremely sensitive to light

achromatic

photoreceptors structure

inner and outer segment connected by cilium

inner - nucleus

outer - light transducing, stacked membranous discs

synaptic terminal makes contact with photoreceptors target cell

types of cones

each contain a visual pigment that is sensitive to different light on the spectrum

fovea composition

higher ratio of cones to rods

ganglion cells have smaller receptive fields

photoreceptors to ganglion cells 1:1

peripheral retina

higher ratio of rods to cones

photoreceptors to ganglion cells >100:1

more sensitive to light

Rhodopsin

visual pigment in rod cells

complex of opsin and retinal

loops across the disc membrane in the outer segment of the rods

opsin

transmembrane protein

makes rhodopsin

retinal

small light absorbing compound

makes rhodopsin with opsin

derivative of vitamin A