Central Nervous System Physiology Flashcards
3 main components of brain
cerebrum, cerebellum, brainstem
Cerebrum
- largest part into two hemispheres
- corpus callosum: links right and left side
- cerebral cortex: grey matter outer layer
- 4 lobes: frontal, parietal, occipital, temporal
- forebrain: cerebrum and diencephalon (thalamus, hypothalamus)
Function of frontal lobe
personality, emotions, control of movement
Functions of parietal lobe
mediates skin and muscle sensation
Functions of occipital lobe
vision
Functions of temporal lobe
hearing and memory functions
Cerebellum
- base of cerebrum
- controls balance and voluntary movements, coordination learning, eye movements
Brainstem
- composed of midbrain, pons, medulla oblongata
- controls respiration, locomotion, cardiovascular, digestion, sleep/wake cycle, arousal, balance posture
Functions of cerebral cortex
sensory perception, motor control, language, cognitive functions
Functions of basal ganglia
movement initiation, inhibition of muscle antagonistic
part of extrapyramidal system
large nuclei deep within cerebral hemisphere
Functions of thalamus
sensory switchboard which selects and relays sensory signals to cortex
Functions of hypothalamus
homeostasis, emotions
Functions of spinal cord
locomotor pattern generator
Functions of the limbic system
learning, emotion, appetite, sex function, endocrine hormone
Parts of the limbic system
thalamus, hypothalamus, hippocampus, olfactory bulbs, septal nuclei
Layers of the meninges
Dura mater - tough outer layer
Arachnoid mater - spidery intermediary mesh
Pia mater - delicate inner layer
Meningitis
infection of the meninges
Cerebrospinal Fluid
- produced in brain ventricles
- reabsorbed into blood in the venous system
- maintains electrolyte balance around neurons
- bather and support neural tissue
Hydrocephalus
water on the brain, reabsorption of CSF is blocked and accumulates
4 types of glial cells
Astrocytes, oligodendrocytes, ependymal cells, microglia
Astrocytes
- physically support neurons by forming scaffold that holds them together
- form blood brain barrier
- form scar tissue which inhibits axon regeneration
- recycles neurotransmitter
- maintain electrolyte balance
Oligodendrocytes
- form myelin sheath around neuronal axons
Ependymal cells
produce cerebrospinal fluid
Microglia
scavengers that ingest bacteria and cellular debris
Where do brain tumors arise from?
glial cells - gliomas
meninges - meningioma
Capillaries of the blood brain border
- tightly joined and less porous
- protects neurons from chemical fluctuations
- oxygen can cross but large molecules cannot (only through carrier-mediated transport systems)
- can block beneficial drugs
Vertebra column
boney structure that supports the trunk, head, leg
within the vertebrae is the spinal canal where spinal cord is found
Spinal cord
- conveys signals from sensory receptors to the brain and signals from brain to effector organs
- neuronal circuitry which generates reflexes and simple rhythmical movements
- 31 pairs of spinal nerves - dermatome
“You can only control what you sense”
in sensory inputs are lost, control is severely affected
Dorsal root ganglion
cluster of sensory neuron cell bodies
Ascending sensory axons
from dorsal columns going up to brainstem carrying sensory info to the brain
Descending sensory axons
afferent axons travelling towards the tail
Ventral horn
efferent axons of motoneurons leave spinal cord to innervate muscles
Dermatomes
cervical nerves - mediate sensory input from the arms
thoracic nerves - mediate sensory information from the abdomen (trunk)
lumbar, sacral, coccygeal nerves - mediate sensory info from the legs and feet
Shingles
neurons in dorsal root ganglia become infected with chicken pox virus
results in band of soreness and pain in the dermatome
Spinal cord injury
when spinal cord is damaged or severed, sensation and motor functions below that level are absent or abnormal
Quadriplegia
spinal damage at C6 or C7
Paraplegia
spinal damage at L1 or L2
Modality (sensory stimulus processing principle)
type of sensory info that is transmitted
structure of sensory receptor determines different stimulus
Meissner’s corpuscles
complex bulbous receptor spiraled into capsule
respond to light touch of skin
Merkel’s corpuslces
respond to touch
Free nerve ending
respond to pain
Pacinian corpsucles
slippery layers called lamellae that slide over each other
respond to vibration
Ruffini corpuscles
respond to skin stretch or temperature
warm receptors - increase firing rate as temp rises
cold receptors - decrease firing rate as temp falls
Type A sensory receptors
axons project directly to the spinal cord
Type B sensory receptors
first order receptor cells respond to stimuli and activate second order cells to CNS
Somatosensory receptors
cover surface of body and signal sensory modalities to CNS
Mechanoreceptors
sense local tissue deformation in skin
Thermoreceptors
sense temperature in skin and brain
Nocireceptors
sense pain in skin, viscera, muscle
Proprioceptors
sense movement and force in muscles and joints
Vestibular receptors
sense head acceleration and tilt
Intensity (sensory stimulus processing principle)
as stimulus intensity increases, membrane potential at initial segment of afferent axon increases until action potentials are generated
recruitment - number of sensory receptors that are activated increases
Neural coding
frequency coding - the bigger the stimulus, the more membrane channels in sensory ending are distorted, the greater number of action potentials
population code - the bigger the stimulus, the more sensory neurons are recruited into activity
temporal pattern code - bursts vs steady firing may mediate certain types of sensations
Duration (sensory stimulus processing principle)
slowly adapting receptors - tonic receptors, generation action potential throughout duration of stimulus (Merkel, free neuron ending, Ruffini)
rapidly adapting receptors - respond only briefly each time stimulus changes (Pacinian and Meissner)
Location (sensory stimulus processing principle)
neuronal signals of given modality from particular part of the body travel along sensory axons in specific tracts in the spinal cord to the brain
Acuity
the ability to tell the difference between things that are close together
lateral inhibition focuses ascending sensory signals enhancing acuity
Two-point discrimination
tightly packed receptors, receptive fields are small and acuity is high (hands and face)
loosely packed receptors, receptive fields are large and acuity is low (abdomen, limbs)
Overlapping receptive fields
when stimulus is applied to any area of the skin, it will always excite more than one receptor
receptive fields that are directly in line with stimulus are excited more and higher action potentials
Divergence
each sensory afferent sends branches to many neurons in the CNS
Convergende
a given neuron in the CNS receives inputs from many sensory afferents
Lateral inhibition
the most active and effected fibers cause the greatest inhibition of adjacent fibers
focuses activation of the neurons on the center of a stimulus (perceived more accurately)
Sensation and perception (sensory stimulus processing principle)
sensation - the conscious awareness of a stimulus
perception - when a sensation is combined with an understanding of its meaning
Topographic map
sensory cortex devoted to input from fact and hands is much bigger than input from abdomen, legs, and feet
homunculus - little man, body parts distorted to represent somatosensory cortex
plasticity - map changes
Descending inhibition
brain and brainstem can screen out certain types of sensory info by inhibiting neurons in afferent pathways
presynaptic and postsynaptic inhibition
Presynaptic inhibition
reduces transmitter release at synapse between first-order and second-order sensory neurons
inhibits specific sensations like pain
several milliseconds
Postsynaptic inhibition
hyperpolarizes the membrane of second order sensory neurons to move membrane potential further away from threshold
less selective
1 millisecond
Pain pathway
tissue damage - prostaglandins and histamine to pain receptors - substance P release in spinal cord - activates projection neurons - signals pain neurons in thalamus and cortex - sensation of pain
Analgesia
suppression of pain transmission
Aspirin
blocks production of prostaglandins that are released by damaged tissue
Gabapentin
blocks production in the nociceptive afferents
Opioids (morphine)
in the CNS, blocks release of substance P onto projection neurons in the spinal cord
Fright, flight, fight response
endogenous opiates neurotransmitters are released so that nociceptive input is reduced
Projection neuron inhibition
by sensory input from large sensory afferents
acupuncture, rubbing the skin, and transcutaneous electrical stimulation (TENS)
Referred pain
the sensation of pain is experienced at a site other than the injured or damaged tissue
sensory afferences from the viscera and internal organs enter the spinal cord and synapse onto the same interneurons as sensory afferents from the skin
Anterolateral system referred pain
pain and temperature
pathway crosses over within a vertebral segment upon entering the spinal cord
Dorsal column system referred pain
touch, pressure, stretch
pathway crosses over in the brain stem to the contralateral side of nervous system
Supraspinal centers controlling movement
sensorimotor cortex, brainstem, cerebellum, cerebral cortex, thalamus, basal ganglia
Feedback control
in spinal cord, actual position of the limb is subtracted from the desired position. the difference causes motor neurons to contract the muscle to minimize that difference
Muscle spindle
- signals length of a flexor muscle
- inside belly of the muscle
- group 1 A (muscle and tendon vibration) and 2 sensory afferents
- sensory ending of muscle spindles are spiraled around these intrafusal muscle fibers
- tissue capsule
Golgi tendon organs
- signals force in a extensor muscle
- tendinous fascicles at the ends of muscle fibers
- group 1 B sensory afferents
Spasticity
overactive stretch reflexes
Extrafusal muscle fibers
main muscle fibers outside muscle spindle that produce measurable force
Alpha motor neurons
activate main muscle extrafusal fibers to contract
Gama motor neurons
activate intrafusal muscle fibers at each end of spindle
stretched the elastic non-contractilePa middle part where sensory endings are located, causing rapid firing
Passive stretching
GTO afferents respond to small increases in their rate of firing
Muscle contraction
contraction of extrafusal muscle fibers causes GTO to fire more rapidly, force in the tendon of contraction muscle is much higher
Muscle spindle feedback reflex
resists the increase in length by reflexly activating extensor motor neurons
GTO feedback reflex
resists the increase of force by reflexly inhibiting the extensor motor neurons
The stronger the spindle reflex, the _____ the spring
stiffer
The stronger the GTO reflex, the _____ the spring
more compliant
Corticospinal tract (CST)
- pyramidal tract
- conveys signals from the sensorimotor cortex through the brainstem to the spinal cord
- crosses to the contralateral side of nervous system at brainstem
- monosynaptic connections with spinal alpha motoneurons
- one neuronal synapse away from muscles
Hemiplegia
inability to move the limb on the contralateral side of the body
Hypertonus
excessive level of skeletal muscle tension or activity
Dysarthria
speech deficits
Aphasia
inability to understand the meaning of sensory inputs or defect in language
Apraxia
problem using day to day objects
Hemi-neglect
occurs when patients fail to be aware of items to one side of their body
Speech
- controlled by left side in most people
- Broca’s and Wernicke’s area
Broca’s area
- motor aspects of speech
- lesions result in motor aphasia (slurring speech)
Wernicke’s area
- comprehension of language
- association of visual, auditory, tactile input with words
- lesions results in sensory aphasia (difficulty understanding the meaning of sensor inputs) and dyslexia (difficulty in reading aloud fluently)
Cerebrum
inputs: sensory input from spinal cord and motor commands from cerebral cortex
vermis: posture, control of movements of neck and trunk
intermediate zone: locomotion control
lateral zone: coordination complex, movements of arms hands fingers
Flocculonodular lobe: controlling balance
Parkinson’s disease
lesion in basal ganglia
poverty of movement (bradykinesia) and rigidity and tremor
Huntington’s chorea, Tourette’s syndrome, hemiballismus
too much movement (dyskinesia
Brainstem
- supplying neurotransmitters to different parts of brain
- control of respiratory and cardiovascular musculature
- control transmission in sensory, motor, reflex, and pain pathways
- initiation of locomotion
Electroencephalogram (EEG)
monitors electrical activity in the brain
amplified voltage fluctuations are recorded between pairs of electrodes on the scalp
summated synchronous post-synaptic potentials of many neurons
used to very brain death
N1
- light sleep
- alpha waves
- reduced frequency and amplitude
- some theta waves
N2
- further lack of sensitivity
- alpha waves replaced by random waves of greater amplitude
- sleep spindles - large amplitude and high frequency bursts
N3
- deep sleep
- more theta and delta activity
REM
- dreaming and rapid eye movement
- most relaxed muscles
- very active brain
- mimic activity of alert awake state
- beta rhythm
Sleep cycle
8 hours - 5 cycles of deep and light sleep (90 minutes each)
time spent in REM increases as morning approaches
N1 –> N2 –> N3 –> REM
Epileptic seizures
voltage fluctuations become very large
Glasgow coma scale
- classify level of consciousness of a person
- eye movements, responses to questions, voluntary movements and can obey commands to move limbs
Criteria of brain death
- the nature and duration of the coma must be taken
- cerebral and brainstem functions are absent
- supplementary criteria includes a flat EEG for 30 minutes
Reticular activation system (RAS)
- during wakefulness - inputs activate neurons in RAS
- neurons release monoamines (norepinephrine, serotonin, histamine) to hypothalamus
- hypothalamus supplies orexins to thalamus and cortex to maintain wakefulness
Suprachiasmatic nucleus
- in morning: activates orexin-producing neurons
- in night: secretes melatonin
- set circadian rhythm
Sleep centre
- pre-optic nucleus of hypothalamus
- activated by increase in adenosine blood concentration
- causes GABAergic inhibition to RAS and reduces orexin levels
Orexin-producing neurons are activated by
- suprachiasmatic nucleus
- negative energy balance
- low blood glucose
- limbic system activity
Limbic system
memory and motion and triggers the drive to explore and move
Characteristics of consciousness
awareness of time, awareness of sensory inputs, fatigue, thirst, happiness, memories, reasoning, ideas
Selective attention
attention shifts from one focus to another
coincident attractors (visual and auditory) are more like to trigger a shifts than separate attractors
thalamus and locus ceruleus in RAS
Conscious perception
specific sets of neurons in different parts of the brain temporarily function together to generate consciousness
central brain area selects and illuminates a temporary set
Hemi-neglect
destruction of specific brain area
the person is unaware oh half of their visual field
Motivation
reward
pathway in the brainstem nuclei releases dopamine within the frontal love
Primary motivated behaviour
directly related to homeostasis
water balance, nutrition, body temp
Secondary motivated behaviour
results in pleasure
can be advantageous or disadvantageous
Emotion
internal attitudes towards events and environment
different part of brain controls different emotions
Depression
maintain levels of serotonin and norepinephrine in synapses in CNS
neurogenesis (generation of new neurons)
Drug dependence
There are 7 criteria and substance dependence is diagnosed when three or more criteria occur within a year
Working memory
- short term, easily acquired, quickly lost
Episodic: recent events, places
Visuo-spatial: recent sights, locations
Phonological: recent words, sounds
Long-term memory
- slow period of acquisition, lasts for much longer, even a lifetime
Declarative (consciousness) - semantic: facts
- episodic: personal experiences
Procedural (motor, subconscious) - stimulus-response behaviours
- motor skills
Caudate nucleus
- part of basal ganglia
- involved in consolidating stimulus to response to behaviors such as those that occur during operant conditionion
- solving sequence tasks
Amnesia
absence of memory
concussion: brain injury measured by type and duration of amnesia
Retrograde
loss of memory of events prior to injury
Aterograde
loss of memory of events after the injury
Korsakoff’s sydrome
damage of hippocampus
compete anterograde amnesia
Alzheimer’s disease
degeneration of memory-holding neurons
maybe due to amyloid precursor proteins that cause excitotoxicity
