Human Phys Exam II

Central Nervous System

Central Nervous System

brain and spinal cord; receives input from sensory neurons and directs the activity of motor neurons

spinal cord

brain stem

cerebellum

cerebrum

cerebral cortex

cerebral cortex, composed of gray matter and underlying white matter. The cerebral cortex is characterized by numerous folds and grooves "

“bark” of the brain -- where cerebral neurons are located

gyrus

An elevated fold

sulcus

the depressed groove between two gyri

Ventricles

cavities of the brain filled with cerebral spinal fluid

Central canal

cavity of the spinal cord filled with CSF

spinal nerves

Each spinal nerve is a mixed nerve composed of sensory and motor fibers

cranial nerves

Cranial nerves are classified as either sensory, motor, or mixed

Know the 4 lobes of the brain

central sulcus

separates parietal and frontal lobes

lateral sulcus

separates frontal lobe from temporal lobe

motor and somatosensory cortex

visual receptive field

the part of the visual field that affects the activity of a particular ganglion cell can be considered its receptive field

photoreceptors

in the retina (rods and cones) and synapses with other neurons in the retina

respond to light

photoreceptor mechanism

Chemical interaction affects ionic permeability of sensory cells

chemoreceptors

sense chemical stimuli in environment or blood. Examples are taste buds, olfactory epithelium and aortic and carotid bodies

chemoreceptors mechanism

Chemical interaction affects ionic permeability of sensory cells

thermoreceptors

respond to heat and cold

receptive field of a neuron serving cutaneous sensation

the area of skin that, when stimulated, changes the firing rate of the neuron

mechanoreceptors

stimulated by mechanical deformation of the receptor plasma membrane

examples are touch and pressure receptors in the skin and hair cells within the inner ear

mechanoreceptor mechanism

Deforms plasma membranes of sensory dendrites or deforms hair cells that activate sensory nerve endings

nociceptors

pain receptors that depolarize in response to stimuli that accompany tissue damage

nociceptors mechanism

Damaged tissues release chemicals that excite sensory endings

proprioceptors

includes the muscle spindles, Golgi tendon organs, and joint receptors. These provide a sense of body position and allow fine control of skeletal movements

Somatotopy

Cortical neurons are arranged in same topology as peripheral receptive fields on the skin, to make up homunculus. Areas with denser receptive fields have bigger cortical representation (more neurons dedicated to processing)

tonotopy

Transduction of sound frequency into spatial location

In cochlea, the apex is thick and responds to low freq

base is thin and responds to high freq

rapidly adapting (phasic)

responds best to onset and offset of stimulus

slowly adapting (tonic response)

continue to respond to continuous stimulus

feature extraction

this concept includes knowing when is vertical, horizontal, and oblique in your hand. Or when your body knows where and how to reach something using your proprietors and visual input. Or when hear something and visual input helps you understand what they are saying. Another example is smelling popcorn and remembering a random movie

dorsal root

composed of sensory fibers

ventral root

composed of motor fibers

dorsal root ganglion

contains the cell bodies of the sensory neurons.

ventral horn of spinal cord

the cell bodies of lower motor neurons are located here

anatomy of spinal cord

Two-point Touch

determines density of receptive fields. Two points are put on skin and when the subject can distinguish its two points, the mm apart tells the receptive field. ie 2mm on thumb = small and abundant receptive fields. Compared to the 42 mm of the back which shows less frequent receptive field

dermatome

each spinal sensory nerves have a receptive field .

One DRG approx. for each vertebra: receptive fields of one DRG = dermatome

shingles/chicken pox

Infection by neural virus (herpes zoster) that lives in DRG cells

Hair Cells of inner ear

Mechanoreceptors that detect vibration (audition)

Bending of stereocilia (due to vibration) opens K+ channels. Because endolymph is high in K+, K+ rushes into hair cell to cause depolarization=action potentials

Utricle

detects linear acceleration, using otoliths as inertial mass to detect gravity and starting/stopping during linear motion

semicircular canals

detect rotational acceleration in each of 3 planes. Sloshing of endolymph around the canal; deforms cupula which bends hair cells.

the cochlea and vestibular apparatus of the inner ear

basic anatomy of the outer, middle, and inner ear

Understand the frequency response of the basilar membrane

Vibrations of oval window -> vibrations in endolymph -> vibration of basilar membrane

frequency response of the basilar membrane

Response of basilar membrane varies across its length. Low frequency sound vibrates apex of cochlea. High frequency sound vibrates base of cochlea

Receptive Field of Auditory Neuron

tuned to characteristic frequency. Neuron’s response (rate of action potentials) reflects intensity of sound at characteristic frequency

Cochlear Implants

reproduce function of basilar membrane and hair cells: stimulate auditory nerve endings at appropriate point in cochlea to reproduce tonotopic mapping of missing hair cells

Rods vs Cones

Because bipolar cells receive input from the convergence of many rods (a), and because a number of such bipolar cells converge on a single retinal ganglion cell, rods maximize sensitivity to low levels of light at the expense of visual acuity. By contrast, the 1:1:1 ratio of cones to bipolar cells to ganglion cells in the fovea (b) provides high visual acuity, but sensitivity to light is reduced"

Bipolar cells

synapse onto ganglion cells

Ganglion cells

project to brain via optic nerve (cranial nerve 2)

Optic Disk

the blind spot, Optic Nerve leaves eye and central artery & vein enter eye and interrupts retina, so no photoreceptor cells

Cones

contain photopigment photopsins: either S (short blue), M (medium green) or L( long red) High-light level, high density in fovea, so detail vision

Rods

contain light-sensitive photopigment protein rhodopsin; grayscale, low-light level, night vision, peripheral vision

Summary of Dark Current & Activation of Rhodopsin

1. Rod Photoreceptors have cGMP-gated Na+ channels on their plasma membrane.

2. In the dark, cGMP levels are high, so Na+ channels are open.

3. In-rush of Na+ depolarizes photoreceptor cell, so it releases more neurotransmitter in the dark.

4. Light activates rhodopsin in the disk membranes by altering configuration of retinal (vitamin A).

5. Rhodopsin is a G-protein coupled receptor (activated by light, not a ligand). Activated G-proteins activate a phosphodiesterase that breaks down cGMP.

6. So in light, cGMP levels fall. cGMP-gated Na+ channels close.

7. Photoreceptor cell becomes hyperpolarized, so it releases less neurotransmitter in the light.

On center ganglion cells

firing increases when light is shown in the center

off center ganglion cells

increases firing with surround illumination

black and white slide

left vison goes to

right cortex

right vision goes to

left cortex

lesion at retina

cut at left optic nerve

cut at left optic tract

loss of left visual cortex

cut at optic chiasm

sympathetic nervous system

fight or flight

Nerves from spinal cord run to chain ganglia or collateral ganglia and then to glands and smooth muscle

parasympathetic nervous system

rest and digest

Nerves from brainstem and spinal cord run to glands and smooth muscle

Sympathetic nervous system neurotransmitters

Preganglionic nerves release Acetylcholine (ACh) to stimulate nicotinic receptors

Postganglionic cells release Norepinephrine (NE) to stimulate or inhibit target tissues via adrenergic receptors

exception: sympathetic fibers to sweat glands use ACh.

Parasympathetic nervous system neurotransmitters

Preganglionic nerves release Acetylcholine (ACh) to stimulate nicotinic receptors

Postganglionic cells release Acetylcholine (ACh) to stimulate or inhibit target tissues via muscarinic receptors

atropine

blocks muscarinic receptors (what’s used at the opthamlogist)

alpha and beta blockers

blocks adrenergic receptors

examples of sympathetic nervous

system affects the body

bronchi dilate, heartbeat increases, blood flow to the muscles, pupil dilate,

example of parasympathetic nervous system

bronchi constrict, pupils constrict, digestion

Know the (general) location of the preganglionic cell bodies and the ganglionic cell bodies

Paraganglion cell bodies are in the spinal cord/brain stem.

Ganglionic cell bodies are in the ganglia.

Adrena medulla

releases norepinephrine and epinephrine when stimulated by the sympathetic ; adrenal medulla are embryologically related to postganglionic sympathetic neurons,

pupil dilation

Sympathetic nerves cause dilation of pupil by stimulating pupillary dilator muscle (NE beta-adrenergic receptors)

pupil constriction

Light via optic nerve (II) stimulates parasympathetic nerve (III) to constrict pupillary sphincter muscle (ACh muscarinic receptors)

Hidrosis

Sympathetic postganglionic neurons synapse onto sweat glands in the skin Sympathetic neurons release ACh (not NE) to stimulate sweating

Horner’s Syndrome

Damage to sympathetic nerves on one side of neck Unilateral (one-sided) constriction of pupil, anhydrosis (lack of sweat), flushing

Organophosphates

insecticides that block cholinesterase enzyme -> enhanced ACh neurotransmission at all synapses Treated with atropine to block effects of elevated ACh

the pupil receptors

muscarinic ACh (constriction) vs

beta-adrenergic receptors (dilation)

adrenal gland receptors

nicotinic Ach receptors

heart receptors

muscarinic Ach (slow)

beta-adrenergic receptors (speed up)

sweat gland receptors

muscarinic Ach receptors

sympathetic chain ganglion receptors

nicotinic Ach receptors

parasympathetic ganglion receptors

nicotinic Ach receptors

cocaine

enhance adrenergic receptors

The cell bodies of the parasympathetic preganglionic neurons are located in the:

brainstem and spinal cord

The cell bodies of the sympathetic preganglionic neurons are located in the:

spinal cord

If the setpoint for body temperature is elevated above normal, then a person will:

feel cold, start shivering, put on a sweater

Meissner’s Corpuscle

small receptive field with rapid adaption

Pacinians’s Corpuscle

Large receptive field with rapid adaption

Merkels Disk

small receptive field, slow adaption

Ruffini’s ending

large receptive field with slow adaption

small receptive field size =

responds to light touch

large receptive field size=

deep receptors responds to stronger force

central sulcus

separates frontal and parietal lobe

Motor cortex

located in front of central sulcus