nervous system Flashcards
central nervous system components
brain and spinal cord
Peripheral nervous system components
- cranial nerves and branches
- spinal nerves and branches
- ganglia
- sensory receptors
Neuron structure
Dendrites - receive input from other neurons
Cell body - cellular functions
Axons - carries electrical signals to terminals + release neurotransmitters
Sensory neuron functions
detect changes in the external and internal environment
Motor neuron functions
controlling muscles or glands
Interneuron function
processing of information from CNS into motor neurons
4 main types of neuroglia in CNS
- astrocytes
- oligodenrocyte
- microglial
- ependymac
astrocytes - CNS
help maintain the appropriate chemical environment
oligodendrocytes - cns
produce the myelin sheath that surrounds axons - action potential.
microglia - CNS
act as immune cells in the CNS, destroying foreign organisms and damaged nervous tissue.
ependymal cells- CNS
responsible for the production of cerebrospinal fluid.
Schwann cells - PNS
produce a myelin sheath that wraps around axons of PNS neurons
Satellite cells - PNS
provide structural support and aid in the exchange of nutrients between neurons and the interstitial fluid
Myelinated vs unmyelinated
myelinated - fast conduction velocity
unmyelinated - slow conduction velocity
sodium-potassium pump
3 Na+ and 2 K+ = to achieve resting membrane potential.
Potassium leak channel
allows potassium to move down its concentration gradient and out of the cell
How is resting membrane potential established?
- K+ wants to move down the concentration gradient out of cells through K+ leak channels.
- Leave the inside more negative
- Eventually, the negative charge inside become so great, it resists the movement of K+ out of the cell. Negative attracts positive.
Graded potentials
a small deviation from the resting membrane potential of the neuron. Can make the cell more negative - hyperpolarizing and depolarising more positive.
summation
process in which graded potentials occurring close enough in time to each other can add together to produce a bigger change in the membrane potential
Voltage-gated channels
proteins that respond to changes in membrane potential by opening a channel in the membrane. Allows ions to move down their concentration gradient.
Action potential threshold
where voltage-gated sodium channels open.
An influx of Na+ onto the cell through these channels = action potential.
Role of CNS
- detects changes in the outside and inside environment
- controls the body’s responses to external and internal changes
- gernates emotions, memories, plans
Cranial meninges
surrounds and protects the brain
spinal meninges
surround and protects the spinal cord.
meninges layers
- dura mater
- Arachnoid mater
- Pia mater
Dura mater
most superficial and strongest layer
- composed of dense irregular connective tissue
- adheres to the interior surface of cranial bones
Arachnoid mater
- below dura mater
- an avascular covering (no blood)
- Between the two layers lies space with interstitial fluid
Pia mater
innermost membrane
- adheres to the surface of the brain and spinal cord
- between the arachnoid mater and the pia mater is the subarachnoid - filled with cerebrospinal fluid
Blood-brain barrier
- tight cell junctions between the endothelial cells of capillaries supplying the brain
- prevents the flow of many substances from the bloodstream into the interstitial fluid in the CNS
Cerebrospinal fluid + functions
the fluid that circulates through cavities in the brain/spinal cord.
- Mechanical protection = serves as shock-absorbing medium that protects the brain/spinal cord from hitting the walls of cranial cavity and vertebral canal.
- Chemical protection = provides the optimal chemical environment for neuronal function
- Circulation = provides a medium for the exchange of nutrients and wastes between the blood and the nervous tissue of the brain/spinal cord.
choroid plexuses
- where csf is formed
- network of capillaries in the walls of the ventricles
- filter the blood plasma and secrete the newly formed cerebrospinal fluid into the ventricles.
cerebral cortex
- region of grey matter that forms the outer portion of the cerebrum
- responsible for most of our ‘higher-level’ brain functions
gyri
folds of the cortex
fissures
deeper grooves
sulci
shallow grooves
functions of the cerebral cortex
- processing of incoming sensory information
- initiation of voluntary movement
- integration of information for complex functions e.g. memory
somatosensory area
parietal lobe
visual area
occipital lobe
auditory lobe
temporal lobe
motor area
frontal lobe
association tract
these contain certain axons that project between gyri of the same hemisphere
commissural tract
these contain axons that project from gyri in one hemisphere to the corresponding gyri in the other hemisphere
projection tracts
these contain axons that project from the lower parts of the brain up to the cerebral hemisphere
Thalamus
located in the cerebrum
- the relay and processing of both sensory and motor information
Hypothalamus
Below the thalamus
- maintenance of homeostasis and body functions
Brainstem
- midbrain
- the pons
- medulla oblongata
- controls involuntary visual (breathing,bp) and auditory reflexes
Cerebellum
- located in the posterior + inferior aspect of the cranial cavity
- monitors and evaluates voluntary movements of skeletal muscoa
- maintains posture and balance
spinal nerve roots
- points where bundles of axons that make up the spinal nerves connect the spinal cord.
- Posterior root = cell bundles of sensory neurons
- Anterior root = axons of motor neurons
Spinal chord function
- Propagation of nerve impulses from the brain to the body, and from the body to the brain.
- The integration of sensory and motor information e.g. reflexes
Cranial nerves
- nerves that arise from the brain
- pass through various foramina (holes) in the cranial bones to innervate parts of the body
- PNS
- motor and sensory neurons
sensory neurons
- olfactory nerves
- optic nerve
- vestibulocochlear nerve
Olfactory (1)
- entirely sensory neurons
- formed by the axons arising from olfactory receptors
- conduct nerve impulses for the sense of smell
Optic (2)
- entirely sensory axons
- formed by axons arising from retinal ganglion
- conducts nerve impulses related to vision.
Oculomotor nerve (3)
- motor/sensory axons
- sensory axons = convey information related to the position of extrinsic eyeball muscles (proprioception)
- Motor axons = convey information for the movement of the eyeball and upper eyelid.
Trochlear nerve (4)
- Mixed nerve
- sensory axons = convey information related to the position of extrinsic eyeball muscles (proprioception)
- Motor axons = convey information for the movement of the eyeball and upper eyelid.
Trigeminal nerve (5)
- largest of the cranial nerves
- sensory axons = convey information relating to touch, pain and temperature
- motor - convey info
Abducens nerve (6)
sensory = info relation of the position of eye muscles motor = movement of the eyeball
The facial nerve (7)
sensory = related to taste and muscle of the face/scalp Motor = convey info. for the movement of a muscle of the face/scalp.
Vestibulocochlear (8)
pure sensory nerve
2 branches
- Vestibular branch carries information related to equilibrium (balance)
- Cochlear branch = carries information related to hearing
The glossopharyngeal nerve (9)
Sensory = carries info. related to taste, swallowing, bp, and blood gas levels. Motor = control swallowing muscles
Vagus nerve (10)
The only cranial nerve extends beyond the head and neck.
Sensory = taste, proprioception of neck/throat, bp, respiration, organs of thoracic.
Motor = speech and swallowing
The accessory nerve (11)
Sensory = proprioception of neck muscles Motor = control of swallowing and head movements
The hypoglossal nerve (12)
sensory = proprioception of tongue muscles Motor = control of tongue muscles related to speech and swallowing
Spinal nerves
connect the CNS to sensory receptors, muscles and glands in all parts of the body
31 pairs
Rami
spinal nerves form branches
Posterior rami (dorsal)
serves muscles and skin of the posterior trunk of the body
Anterior rami (ventral)
serves muscles and structures of the upper and lower limbs. Also serves the skin of the lateral and anterior trunk.
Plexus
a network formed by axons of adjacent nerves
- made up of axons derived from a number of spinal nerves = meaning damage to a single level of the spinal cord is less likely to end in paralysis
cervical plexus
supplies the skin and muscles of the head, neck and superior portions of the shoulders and chest
Brachial plexus
nerve supply for the shoulder and upper limbs
lumbar plexus
provide the nerve supply to the anterior and lateral abdominal wall, external genitals, and part of the lower limbs
sacral plexus
provide nerve supply to buttocks and lower limbs
What is a reflex?
the fast, involuntary sequence of actions that occur in response to a specific stimulus.
Cranial reflex
the integration of information performed by the CNS occurs in the brainstem. e.g. tracking eye movements
Spinal reflex
integration of information performed by the CNS occurs in the grey matter of the spinal cord. e.g. jerking of hand
Somatic reflex
contraction of skeletal muscle
automatic reflex
responses of smooth muscles, cardiac muscles and glands
stretch reflex
- results in a contraction of a skeletal muscle in response to the stretching of that muscle.
- involves reflex arc = single sensory neuron synapses with a single motor neuron
- shown by tapping tendons attached to muscles at the elbow, wrist, knee and ankle
Patella stretch reflex
- a stretch of a tendon activates sensory receptors that monitor the length of muscles
- Stimulation of the muscle spindle activates sensory neurons that send information to the grey matter of the spinal cord.
- Integration occurs in the grey matter - the sensory neuron activates a motor neuron.
- Impulses travel down the motor neuron axon towards the effector (the muscles).
- Impulses from the motor neuron stimulate the muscle causing it to contract. - monosynaptic route but must turn off antagonistic muscle at the same time.
A reflex that turns off these antagonistic muscles
Polysynaptic circuit. the sensory neuron activates inhibitory neuron.
