Physiology of Neurological System

high degree of visual acuity in

central retina

sensory signals enter the cord and go to 2 separate destinations

gray matter

higher levels (brainstem + cortex)

anterior motor neurons are located in each segment of

anterior horns of gray matter cord

classification of neurons

sensory, motor, interneurons

types of anterior motor neurons

alpha motor neurons and gamma motor neurons

difference between alpha and gamma motor neurons

alpha - large skeletal fibers

gamma - smaller skeletal (intrafusal) fibers

which type of neurons are in the gray mater, small and excitable and spontaneous firing

interneurons

The interconnections among the interneurons and anterior motor neurons are responsible for the

integrative functions of the spinal cord

Renshaw cells

Interneurons that produce recurrent inhibition in the spinal cord (lateral inhibition)

propriospinal fibers

interconnecting different spinal cord levels

The ascending and descending _________ of the cord provide pathways for the multisegmental reflexes

propriospinal fibers

types of muscle sensory receptors

muscle spindle

golgi tendon organs

which part of the intrafusal muscle fiber contracts and which part is the receptor

ends (excited by gamma efferent fibers)

central

muscle spindle receptor can be excited in 2 ways

- lengthening

- contraction of ends

'static vs dynamic response' effect of spindle receptors

both primary and secondary endings continue to transmit signals vs primary endings are dependent on changes in spindle length

gamma motor nerves of muscle spindle divided into

gamma-dynamic (excites nuclear bag intrafusals) + static (excites nuclear chain intrafusals)

monosynaptic pathway of stretch reflex

- proprioceptor in spindle enters dorsal root of cord

- branch goes to ant grey matter

- synapses with ant motor neurons

- motor fibers sent back to muscle

'damping' function of stretch reflexes

prevents jerky movements, signals transmitted in unsmooth form

how are the alpha and gamma motor neurons coactivated in a voluntary motor activity

signals transmitted from brain to alpha motor neurons then gamma motor neurons stimulated simultaneously

brain areas that control gamma motor system

bulboreticular facilitatory region of brainstem (cerebellum, basal ganglia and cortex)

golgi tendon reflex

helps control m tension, stimulated when m fibers are tensed

functions of golgi tendon reflex

inhibitory, prevents muscle tearing or avulsion to bone and equalizes contractile forces of separate m fibers

flexor reflex

the quick contraction of flexor muscles resulting in the withdrawal of a limb from an injurious stimulus

how does afterdischarge affect flexor reflex

relaxation is delayed after stimulus is over (when reflex is fatigued)

crossed extensor reflex

opposite limb supports body during withdrawal of injured limb by interneurons, prolonged afterdischarge

reciprocal inhibition phenomenon

when a stretch reflex excites one muscle, it simultaneously inhibits the antagonist m

Excitation of a single motor cortex neuron usually excites

a specific movement (rather than 1 muscle)

for the premotor area and primary motor cortex, which muscle groups are located laterally and also upwards

lat - mouth + face

up - hand, arm, trunk, legs

mirror neurons in premotor area

active when specific motor task is performed, transform heard/seen acts into motor representations

which area provides bilateral movements + positional movements of head + fine arm movements

supplementary motor area

broca's area of

motor speech

Corticospinal (pyramidal) tract

Higher motor system that humans have that permits discrete and detailed movements (writing)

Betz cells

giant pyramidal cells in primary motor cortex,

incoming sensory fiber pathways to motor cortex

nerve signals from somatosensory + sensory systems (visual + auditory)

incoming fibers to __________:

- cortex

- somatosensory + intralaminar nuclei from thalamus

motor cortex (corticospinal pyramidal tract)

large neurons in red nucleus give rise to rubrospinal tract, which crosses brainstem and courses to

corticospinal tract into lat spinal cord

corticorubrospinal tract

synapses at magnocellular portion of red nucleus and contracts muscles + accessory route for discrete signals

extrapyramidal system

all portions of brain for motor control

___________ signals arise in muscle spindles, tendon organs and tactile receptors of skin

somatosensory

motor control system can be damaged by common abnormality called

stroke

removal of primary motor cortex with Betz pyramidal cells causes

paralysis

________ serves as a station for command signals from higher neural centers and contains motor and sensory nuclei

brainstem (medulla, pons and mesencephalon)

functions of brainstem

cardio + respo + GI systems control, motor, equilibrium and eye movements

reticular nuclei are divided into (+ functions)

pontine reticular nuclei (excites antigravity m)

medullary reticular nuclei (relax)

decerebrate rigidity

characteristic of a corticospinal lesion at level of brainstem, medullary reticular inhibitor system is nonfunctional

Decreasing voltage to a less negative values makes the membrane

more excitable

spinal motor neuron resting membrane potential is

-65 milivolts

sodium and chloride ion conc is high in ________ and low in _______ (K+ is opposite)

extracell fluid

in neuron

purpose of intracellular fluid in neuron

highly conductive, change in potential in any part causes equal change in other parts

3 states of a neuron

1. resting (-65 mV)

2. excited (less negative ~ -45mV from Na influx)

3. inhibited (more negative ~ - 70mV from K efflux and/or Cl influx)

excitatory postsynaptic potential (EPSP)

a slight depolarization of a postsynaptic cell, bringing the membrane potential of that cell closer to the threshold for an action potential

Inhibitory synapses open mainly

chloride channels

Hyperpolarization

potassium efflux which increases intracell neg

inhibitory postsynaptic potential (IPSP)

temporary hyperpolarization (more negative) of a membrane

what happens to the neuronal membrane when excitatory synapse excites the ant motor neuron

membrane becomes highly permeable to sodium ions, rapid influx - EPSP

Most Dendrites Cannot Transmit Action Potentials, but They Can Transmit Signals Within the Same Neuron by

electrotonic conduction (direct spread of electrical current by ion conduction in fluids)

effect of complete cessation of oxygen on neurons

complete inexcitability

Sleep vs coma

sleep is unconsciousness that can be aroused by stimulus, coma cannot be aroused

brain waves of NREM sleep

strong and low frequency

REM sleep is associated with

vivid dreaming and active muscle movements

REM sleep occurs as

bouts, appearing every 90 min

in which sleep is there depressed muscle tone (inhibition of spinal m control areas) but also irregular m movements

REM

in REM sleep, what rates are irregular

heart and respiratory rates

Active inhibitory process theory of sleep

a centre under midpontile level causes sleep by inhibiting other parts of brain

sleep be provoked by stimulation of which parts of brain

raphe nuclei, nucleus of tractus solitarius and diencephalon

lesions in sleep-promoting centers

lesions in raphe nuclei causes high state of wakefulness

muramyl peptide (from CSF) effect on sleep

causes natural sleep when injected

possible cause of REM sleep

acetylcholine

positive feedback activity of wakefulness

sleep centers are inactivated - no inhibition of reticular activating nuclei - excitation of cortex + PNS

Orexin neurons are important for

arousal and wakefulness

principal values of sleep is to restore

natural balances among neuronal centers

alpha waves

the relatively slow brain waves of a relaxed, awake state

•When the awake person's attention is directed to some specific type of mental activity, the alpha waves are replaced by asynchronous, higher frequency but lower voltage _________ waves.

beta

where are alpha waves located

occipital region

beta waves

smaller and faster brain waves, typically indicating mental activity and located at parietal and frontal regions

theta waves

brain waves indicating the early stages of sleep

delta waves

the large, slow brain waves associated with deep sleep

where do delta waves occur

cortex

how is intensity of brain waves from scalp determined

# of neurons and fibers that fire in synchrony

Alpha waves will not occur in the cerebral cortex without cortical connections with

thalamus

Effect of Varying Levels of Cerebral Activity on the Frequency of the EEG

proportional

4 stages of slow-wave sleep according to EEG

1. light sleep, w/ sleep spindles

2,3,4. EEG frequency slows until delta waves

why is REM sleep desynchronized

lack of synchrony in neuron firing, waves are irregular and of high frequency

seizures

temporary disruptions of brain function caused by uncontrolled excessive neuronal activity