Physiology Review Flashcards
What are cells in the motor cortex organized into?
vertical columns
What does each vertical column of cell in the motor cortex stimulate?
A group of synergistic muscles or even a single muscle.
What is each vertical column of cells in the motor cortex divided into?
6 distinct layers
In the motor cortex, which layer is pyramidal cells in?
5th layer
What layers does input signals enter in the motor cortex?
layers 2-4
What do neurons arising in the 6th layer of the motor cortex communicate with?
With other regions of the cerebral cortex.
What are the groups of neurons in the spinal cord?
> sensory (afferent)
anterior motor neurons (efferents)
interneurons
What type of fibers do alpha motor neurons give rise to?
A alpha fibers
What are interneurons responsible for most of in the spinal cord?
spinal cord integrative function
What are the characteristics of interneurons?
> 30X as numerous as anterior motor neurons
small and highly excitable
capable of spontaneous activity
responsible for most of spinal cord integrative function
Where are Renshaw cells located?
anterior horns of spinal cord
What are Renshaw cells?
inhibitory interneurons in the anterior horns of the spinal cord
What do Renshaw cells do?
Transmit inhibitory signals to surrounding motor neurons.
- results in lateral inhibition
- enhance fluidity of limb movement
Transmit inhibitory signals to same motor neuron.
- results in recurrent inhibition
Where do Renshaw cells receive collateral branches from?
alpha motor neurons
What type of cell innervates muscle spindles?
small gamma motor neurons (group II afferents)
What are the two types of intrafusal fibers that make up muscle spindles?
> Nuclear bag fibers
> Nuclear chain fibers
What do nuclear bag fibers detect in the muscle spindle?
Rate of change (dynamic change) in muscle length.
What do nuclear chain fibers detect in the muscle spindle?
Static change in muscle length.
What are nuclear bag fibers innervated by?
group Ia afferents and dynamic gamma efferents
What are nuclear chain fibers innervated by?
group II afferent and static gamma efferents
Which are more numerous, nuclear chains fibers or nuclear bag fibers?
nuclear chain fibers more numerous
How are nuclei arranged in nuclear bag fibers?
multiple nuclei located in a central “bag-like” configuration
How are nuclei arranged in nuclear chain fibers?
multiple nuclei arranged in a single row
In muscle spindles, what transmits dynamic stretch reflex signals?
signals transmitted from primary nerve endings
What action of the muscle elicits a dynamic stretch reflex?
elicited by rapid stretch or unstretch
What is the purpose of the dynamic stretch reflex?
opposes sudden changes to muscle length
What is the purpose of the static reflex?
causes degree of muscle contraction to remain relatively constant
In muscle spindles, what transmits static reflex signals?
signals transmitted by both primary and secondary endings
You know muscle spindles have both a dynamic stretch reflex and a static reflex, but what is the main function of these two components combined?
prevents jerkiness of body movements (damping)
What does muscle stretch lead to?
direct increase in firing rate of type Ia afferent fibers
> group Ia afferents synapse directly on alpha-motor neurons of the same muscle
muscle contracts and decreases tension on muscle spindle
synergistic muscles are activated and antagonistic muscles are inhibited
On which neurons do group Ia afferents synapse directly?
alpha-motor neurons on the same muscle
Talk through muscle spindle function.
Slide 7 in Review
What are the three major motor control areas of the brain?
- motor cortex
- cerebellum
- basal ganglia
What is the function of the premotor and supplementary motor cortices?
Generate a plan for movement.
transfer plan to primary motor cortex
True or False:
Signals generated from the premotor and supplementary motor cortices in generating a plan for movement involves more complex patterns of movement than the more discrete pattern generated by the primary motor cortex.
True
Which part of the premotor cortex develops a “motor image” of the total muscle movement that is to be performed?
anterior part of premotor cortex
Which cortex programs complex motor sequences and is responsible for mental rehearsal for a movement?
supplementary motor cortex
Where is the image located in the motor cortex that excites each successive pattern of muscle activity required to achieve the image?
posterior motor cortex
Which two pathways does the posterior motor cortex send signals to?
1) –> primary motor cortex
2) –> basal nuclei and thalamus –> primary motor cortex –> cortico-spinal pathways down spine
In the pyramidal system, where do upper motor neurons originate?
motor cortices
What percentage of upper motor neurons decussate in pyramids and form the lateral corticospnial tract?
75-85%
Where do the remaining 15-25% of upper motor neurons that don’t deccussate in pyramids to form the lateral corticospinal tracts decussate near?
Near synapse with lower motor neurons and form anterior corticospinal tracts.
What do most upper motor neurons synapse with?
Association neurons in spinal cord central gray.
What are upper motor neurons classified according to?
Where they synapse in the ventral horn.
> medial activation system
lateral activation system
nonspecific activating system
What does the medial activation system innervate?
postural and girdle muscles
What does the lateral activation system innervate?
associated with distally located muscles used for fine movements
What does the nonspecific activating system innervate?
facilitate local reflex arcs
Which two tracts make up the pyramidal system?
> corticospinal tract
> corticobulbar tract
Name the two pyramidal and 3 extrapyramidal tracts that we covered?
> Pyramidal System:
- corticospinal tract
- corticobulbar tract
> Extrapyramidal Tracts:
- rubrospinal tract
- vestibulospinal tract
- reticulospinal tract
Where does the rubrospinal tract originate?
Red Nucleus
Where does the rubrospinal tract decussate at?
in midbrain
Where in the spine does the rubrospinal tract descend?
lateral funiculus (column)
What is the function of the rubrospinal tract?
closely related to cerebellar function
What do patients with a lesion in their rubrospinal tract present with?
> Impairment of distal arm and hand movement.
> Intention tremors (similar to cerebellar lesions).
Where does the vestibulospinal tract originate?
vestibular nuclei
receives major input from vestibular nerve (CN VIII)
Where in the spinal cord does the vestibulospinal tract descend?
anterior funiculus (column)
What does the vestibulospinal tract synapse with?
lower motor neurons to extensor muscles
What is the vestibulospinal tract primarily involved in?
Maintenance of upright posture.
Where does the reticulospinal tract originate?
various regions of reticular formation
In which part of the spinal cord does the reticulospinal tract descend?
anterior portion of lateral funiculus (column)
What is the function of the reticulospinal tract?
Thought to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs.
fills in the gaps
What are the 3 components of the vestibular apparatus?
> utricle
saccule
semicircular canals
In which plane is the macula of the utricle located in?
horizontal plane
In which plane is the macula of the saccule located in?
vertical plane
What does the macula in the utricle do?
plays role in determining orientation of head when head is upright
What does the macula in the saccule do?
signals head orientation when person is lying down
What kind of layer is each macula, both in the utricle and saccule, covered by?
gelatinous layer
What does the macula, both in the utricle and saccule, contain within?
> Contains large number of embedded small calcium carbonate crystals (statoconia).
> Contains thousands of hair cells which project cilia into the gelatinous layer.
What does the weight of the statoconia (small calcium carbonate crystals) do?
Bends cilia in the direction of gravitational pull.
What are the characteristics of hair cells in the vestibular apparatus?
> Has 50-70 small cilia (stereocilia).
> Has 1 large cilium (kinocilium) off set to one side.
> Tips of stereocilia are connected together and to kinocilium.
> Bending of stereocilia toward kinocilium opens hundreds of cation channels (mostly potassium) causing receptor membrane depolarization and excitation.
> Bending of cilia in opposite direction closes channels and hyperpolarizes receptor membrane.
> Hair cells are oriented such that bending the head in different directions causes different groups of hair cells to depolarize.
What is the mechanism of hair cell function in the semicircular canals when you move your head?
> When head begins to rotate in any direction, inertia of the fluid in one or more of the semicircular canals remains stationary while semicircular canal rotates with the head.
> Fluid flows from the duct and through the ampulla and causes the cupula to bend to one side.
> Hundreds of hair cells within each cupula detect this bending and send signals via the vestibular nerve.
What is the function of the hair cell when the head is bend forward 30 degrees?
> lateral ducts are horizontal
> anterior ducts are in vertical planes projecting forward and 45 degrees outward
> posterior ducts are in vertical planes projecting backward and 45 degrees outward
What separates the two hemispheres of the cerebellum?
Vermis
What is each hemisphere of the cerebellum divided into?
- intermediate zone
- lateral zone
What are the 3 lobes that the cerebellum is divided into?
- anterior lobe
- posterior lobe
- flocculonodular lobe
Which lobe of the cerebellum is associated with the vestibular system?
flocculonodular lobe
What is the function of the vermis in the cerebellum?
location for control functions for muscle movements of the axial body, neck, shoulders, and hips
What is the function of the intermediate zone in the cerebellum?
concerned with controlling muscle contractions in the distal portions of the upper and lower limbs, especially - hands, feet, fingers, and toes
What is the function of the lateral zone in the cerebellum?
associated with cerebral cortex with planning of sequential motor movements
What does the cortex of the cerebellum consist of?
Consists of transversely arranged narrow gyri called folia.
What are the characteristics of the cortex of the cerebellum?
Like the cerebral cortex, this is gray matter and consists of multiple layers of cells, dendrites, and synapses.
Which intracerebellar nuclei make up the gray matter of the cerebellum?
- dentate nuclei
- emboliform nuclei
- globose nuclei
- fastigial nuclei
What do lesions in the dentate nuclei, emboliform nuclei, and globose nuclei cause?
extremity ataxia
Where do dentate, emboliform, and globose nuclei fibers project to?
red nucleus
What are motor control are dentate, emboliform, and globose nuclei related to?
Limb musculature and fine manipulative movement.
What do patients with a lesion in the fastigial nuclei in the gray matter of the cerebellum present with?
trunk ataxia
Where do the fibers from fastigial nuclei in the gray matter of the cerebellum project to?
- reticular formation
- vestibular nuclei
What motor activity is the fastigial nuclei located in the gray matter of the cerebellum related to?
Postural activity and limb movements via reticulospinal and vestibulospinal tracts.
What cells are found in the cerebellar cortex?
- granular cells
- golgi cells
- basket cells
- stellate cells
- purkinje cells
Which cell type in the cerebellar cortex form parallel fibers in the cortex?
granular cells
Where do golgi cells project from and to?
From parallel fibers (+); To granular cell bodies (-)
Where do basket cells project from and to?
From parallel fibers; To Purkinje axon hillock (-)
Where do stellate cells project from and to?
From parallel fibers; To Purkinje dendrites (-)
What kind of cells do basket cells and stellate cells provide lateral inhibition to?
Purkinje cells to provide damping.
Which cell supplies the ONLY output from the cortex of the cerebellum?
Purkinje cells
From what fibers do Purkinje cells receive input from?
parallel fibers
20,000 synapses between parallel fibers and one Purkinje cell
True or False:
Output from Purkinje cells to intracerebellar nuclei is always inhibitory.
True
True or False:
Purkinje cells have extensive dendritic branching.
True
Where do climbing fibers originate from?
medullary olives
Where do mossy fibers originate from?
Multiple centers in brainstem and spinal cord, including:
> vestibulocerebellar tract
> spinocerebellar tract
> pontocerebellar tract
Where do mossy fibers synapse?
> multiple synapses on Purkinje cells and result in simple spikes
> granule cells in glomeruli
Does mossy or climbing fibers play a major role in motor learning?
climbing fibers
Do both climbing and mossy fibers make multiple synapses on Purkinje cells?
Yes, but:
> mossy fibers result in simple spikes
> climbing fibers result in complex spikes
Which afferent fibers, climbing or mossy, “condition” the Purkinje cells?
climbing fibers
What neurotransmitter does Purkinje cells use?
GABA - always inhibitory
Where do Purkinje cells axons project to?
> deep cerebellar nuclei
> vestibular nucleus
What is the function of Purkinje cells in the cerebellar cortex?
Modulates output of cerebellum and provides synergy (regulates rate, range, and direction of movement).
What does the vestibulocerebellum consist of?
- flocculonodular lobes
- vermis
What is the function of the vestibulocerebellum?
Control of balance and eye movements.
When did the vestibulocerebellum evolve?
evolved at about the same time as vestibular system
Where does the vestibulocerebellum primarily send output to?
vestibular system
What happens if you lose your flocculonodular lobes in the cerebellum?
extreme disturbance of equilibrium and postural movements
Where does the basal nuclei receive most of its input from?
cerebral cortex
Where does the basal nuclei return most of its output to?
cerebral cortex
What is the principle role of the basal nuclei?
Work with corticospinal system to modulate thalamic output to the motor cortex to plan and execute smooth movements.
What paired nuclei does the basal nuclei consist of?
> striatum - caudate nucleus - putamen > globus pallidus > substantia nigra > subthalamic nucleus
What is the putamen circuit (direct pathway) for?
subconscious execution of learned patterns of movement
In the putamen circuit (direct pathway), what is the overall action of dopamine?
excitatory
True or False:
The IGP/SubNigRet is normally active and sends inhibitory signals to the thalamus.
True
What neurotransmitter does connections between the striatum and the substantia nigra use?
dopamine
Indirect pathway - D2 receptors (-)
Direct pathway - D1 receptors (+)
What does exciting the putamen inhibit?
IGP/SubNigRet and allows the thalamus to send excitatory signals to the motor cortex.
What is the caudate circuit (indirect pathway) for?
Cognitive planning of sequential and parallel motor patterns.
plays major role in cognitive control of motor activity
Is the caudate circuit (indirect pathway) overall inhibitory or excitatory?
inhibitory - tends to decrease control of motor activity
Which neurons are destroyed to cause Huntington’s diseas?
GABA neurons that control the inhibitory signal between the caudate nucleus and the globus pallidus (external).
Thus, indirect pathway no longer has inhibitory influence on direct pathway and motor activity is increased.
What NT does the substantia nigra use to send signals to the caudate nucleus and putamen?
Dopamine
- direct pathway is (+)
- indirect pathway is (-)
What NT does the caudate nucleus and putamen use to send signals to the globus pallidus and substantia nigra?
GABA (inhibitory)
What NT does the cerebral cortex use to send signals to the caudate nucleus and putamen?
acetylcholine (excitatory)
Multiple pathways from the brain stem use what neurotransmitters?
- norepinephrine
- serotonin (inhibitory)
- enkephalin
What doe multiple glutamate pathways provide?
Most of the excitatory signals.
What are the characteristics of a patient with Huntington’s?
- flicking movements of individual muscles
- progressive severe distortional movements of entire body
- severe dementia
- motor dysfunctions
What are the abnormal movements seen in patients with Huntington’s disease most likely caused by?
Loss of most of cell bodies of GABA-secreting neurons of caudate nucleus and putament and of Ach neurons in other parts of the brain.
List the stimulating factors for sweating.
- Stimulation of anterior hypothalaus-pre-optic area in the brain electrically or by excess heat.
- Cholinergic sympathetic nerve fibers (muscarinic).
- Circulating epinephrine and norepinephrine.
What is sweating a major mechanism for?
Heat Loss
What is the concentration of sodium and chloride in precursor secretion?
Na = 142 mEq/L Cl = 104 mEq/L
What are the characteristics of a strong stimulation of sweat glands?
- Large amounts of precursor secretion are formed.
- Ducts reabsorb only about half the sodium chloride.
- Concentrations of sodium and chloride ions are about 50-60 mEq/L.
- Little water is reabsorbed.
What effect does aldosterone have on sweat concentration?
stimulates Na and water reabsorption from sweat glands in exhange for K.
True or False:
The composition of precursor secretion is similar to that of plasma w/o proteins.
True
What are the principle areas of the brain that affect body temperature?
- anterior hypothalamic/pre-optic area
- pre-optic area
The anterior pre-optic area contains both heat-sensitive and cold-sensitive neurons. What do heat sensitive neurons do?
increase firing rate 2-10X in response to a 10 C increase in body temperature
The anterior pre-optic area contains both heat-sensitive and cold-sensitive neurons. What do cold-sensitive neurons do?
increase firing rate when temperature falls
What does heating of the anterior hypothalamic/pre-optic area cause?
- dilation of skin blood vessels over the entire body
- profuse sweating over the entire body
- inhibition of excess heat production
What is the definition of fever?
Fever is defined as a body temperature above the usual range of normal.
What are causative factors of fever?
- brain abnormalities
- surgery in region of hypothalamus
- prostaglandins
- lipposaccharide toxins
How do pyrogens increase the set point temperature?
Increasing production of IL-2 in phagocytic cells.
> IL-1 causes anterior pituitary to produce prostaglandins.
> IL-1, prostaglandins increase the set point temperature.
> Aspirin decreases set-point temperature by inhibiting cyclooxygenase which results in decrease in production of prostaglandins.
Are slow waves action potentials?
No
Do slow waves occur spontaneously?
Yes
In which interstitial cells do slow waves originate?
Cajal cells (pacemakers)
What do slow waves set the maximum frequency of?
Contraction for each part of the GI tract.
True or False:
Slow waves may be caused by complex interactions among the smooth muscle cells and the interstitial cells of Cajal (smooth muscle cell electrical pacemakers).
True
Cells of Cajal undergo cyclic changes that periodically open and produce inward (pacemaker) currents that may generate slow wave activity.
What do slow waves excite the appearance of?
intermittent spike potentials
spike potentials excite the muscle contraction
What do spike potentials excite?
muscle contraction
Are spike potentials true action potentials?
Yes
When do spike potentials occur?
Automatically when resting membrane potential of GI smooth muscle becomes more positive than -40 mV.
What is the relationship between slow wave potential and spike potentials?
Higher the slow wave potential, the greater the frequency of the spike potentials.
How much longer does a spike potential last when compared to a typical action potential in a large nerve fiber?
10-40 times (normal AP = 10-20 seconds)
What are spike potentials responsible for opening in GI smooth muscle cells?
Calcium channels and smaller number of sodium channels.
channels open slowly and close rapidly
What is the stimulus for gastrin secretion?
- small peptides and amino acids in stomach lumen, especially pheynlalanine and tryptophan.
- distension of stomach
- vagal stimulation mediated by GRP (gastrin-releasing peptide)
What inhibits gastrin secretion?
- acid from stomach
- somatostatin
Where is gastrin secreted from?
- G cells of antrum, duodenum, jejunum.
- in response to stimuli associated with ingestion of a meal (e.g., stomach distension or gastrin releasing peptide (GRP))*
What does gastrin do?
- stimulates gastric acid secretion by parietal cells
- stimulates mucosal growth by stimulating synthesis of RNA and new protein
Patients with gastrin-secreting tumors have?
hypertrophy and hperplasia of gastric mucosa
When does Zollinger-Ellison syndrome occur?
From gasatrin-secreting non-beta cell tumors of pancreas.
What stimulates secretion of CCK?
- small peptides and amino acids
- fatty acids and monoglycerides
Where is CCK secreted from?
I cells of duodenum, jejunum, and ileum.
What are the stimulatory actions of CCK?
- stimulates pancreatic enzyme secretion
- stimulates pancreatic bicarbonate secretion
- stimulates growth of exocrine pancreas
- stimulates contraction of gallbladder and relaxation of sphincter of Oddi for secretion of bile
What are the inhibitory action of CCK?
- inhibits gastric emptying
- inhibits appetite
What stimulus causes secretion of secretin?
acid and fat in lumen of duodenum
Where is secretin released from?
S cells of the duodenum, jejunum, and ileum.
What are the stimulatory actions of secretin?
- stimulates pepsin secretion
- stimulates pancreatic bicarbonate secretion
- stimulates biliary bicarbonate secretion
- stimulates growth of exocrine pancreas
What are the inhibitory actions of secretin?
inhibits gastric acid secretion by parietal cells
What is the stimulus for secretion of GIP?
- only GI hormone released in response to protein, fat, and carbohydrate
- released in response to orally administered glucose
What is the site of secretion of GIP?
K cells of duodenum and jejunum.
What is the stimulatory action of GIP?
stimulates insulin release
What is the inhibitory action of GIP?
inhibits gastric acid secretion by parietal cells
Which hormone is the MOST potent factor for control feedback to the duodenum?
CCK
