Anatomy (nervous system) Flashcards
two communication and control systems that keep things working properly
nervous system
endocrine system
how do they carry their messages
they use chemicals to carry their message but they do it by different means and one different timescale
nervous system’s chemical messengers are called
neurotransmitters and they are only produced by neurons (nerve cells)
neurotransmitters
produced by neurons, travels short distances across synapses, allows system to react quickly
synapses
gap/ junction between two neurons or between a neuron and its target cell
chemical messengers of the endocrine system called:
hormones
Hormones
secreted directly into bloodstream, where they travel a long distances to reach their targets, body reacts more slowly to changes
structurally the nervous system has two main divisions:
central nervous system (CNS)
peripheral nervous system (PNS)
CNS
central nervous system
composed of the brain and spinal cord
PNS
consists od cordlike nerves that link the central nervous system with the rest of the body
3 main activities
sensory functions
integrating functions
motor functions
‘neuro’
refers to the nervous system
‘logos’
means the study of
neurons
nerve cells
are the basic, functional unit of the nervous system, high requirement for oxygen, cannot reproduce but can regenerate cell processes (this can take years and can only happen if the nucleus is safe), have support and protection from neuroglia cells vary in appearance for different parts
glial
greek meaning glue
central cell body
soma or perikaryon
cell processes
dendrites and axons
dendrites
receive stimuli or impulses form other neurons and conduct this stimulation to the rest of the body
short, numerous, multi branched
referred to a afferent processe because they conduct impulses towards the cell body, may serve as sensory receptors that receive or sense stimuli such as heat, cold, touch, pressure, stretch, or other physical changes form the inside or the outside the body
axons
conduct nerve impulses away form the cell (efferent) body towards another neutron or effector cell,
short,long process,
maybe covered with myelin (white matter), nerve fibres: bundles of axons
myelinated axons
myelinated axons conduct impulses faster than those with no myelin,
central nervous system (CNS)
- composed of brain and spinal cord
* found along central axis of body
peripheral nervous system (PNS)
- components extend away from the central axis outward
- cranial nerves
- spinal nerve
afferent nerve fibers
- conduct impulses toward CNS
* also called sensory nerves
efferent nerve fibers
- conduct impulses away from CNS
* also called motor nerves
mixed nerves
nerves may contain both kinds of nerve fibers most nerves in the PNS are mixed nerves
autonomic nervous system
- coordination of automatic body functions
* example is stimulating release of digestive juices in response to ingestion of a meal
somatic nervous system
• conscious or voluntary control of skeletal muscles
Resting State
neuron is not being stimulated
Na+ has pumped out of cell
K+ has pumped into cell
net negative charge inside cell membrane
Depolarization
neuron receives external stimulus
Na+ channel opens on neuron cell membrane
Na+ ions flow into cell by passive diffusion
-charge now positive inside cell membrane
-switching of electrical charge from negative to positive is known as an action potential
Beginning of Repolarization
- Na+ channels are closing
- K+ channels are opening
- K+ ions flow out of cell
- net charge is returning to negative direction
Repolarization
sufficient outflow of K+ ions restored net negative charge to inside of cell
Na+ and K+ ions are on opposite sides of cell membrane from where they started
resting state is restored
threshold stimulus
- stimulus is strong enough to cause complete depolarization and to generate a nerve impulse
- all-or-nothing principle
nerve impulse
- electric charges “flip” across cell membrane (depolarization), followed by “unflipping” of the electric charges (repolarization)
- adjacent area is stimulated, spreading a wave of depolarization
Refractory Period
• very brief time period when a neuron is insensitive to additional stimuli • cell is still in depolarization/early repolarization
absolute refractory period
• during Na+ influx and early K+ outflow
relative refractory period
- during end of repolarization period
- possible to stimulate another depolarization if stimulus is very large
Saltatory Conduction
• rapid means of conducting an action potential
- each Na+ channel opening stimulates opening of adjacent channel
- depolarization in myelinated axons can only take place at the nodes of Ranvier
synapse
• junction between two neurons or a neuron and a target cell
synaptic cleft
• gap between two adjacent neurons
presynaptic neuron
- brings depolarization way to synapse
* releases neurotransmitter
postsynaptic neuron
• contains receptors for the neurotransmitter
Synaptic Transmission
- perpetuation of the nerve impulse from one neuron to the next cell
- axon
- telodendron
- terminal bouton (synaptic bulb or synaptic knob)
- vesicles
¥ depolarization wave causes vesicles to dump neurotransmitter into the synaptic cleft
¥ neurotransmitters diffuse across the synaptic cleft toward postsynaptic membrane
¥ receptors on the postsynaptic membrane bind the neurotransmitter
excitatory neurotransmitters
• usually cause influx of Na+ so postsynaptic membrane moves toward threshold,
beginning a new impulse
inhibitory neurotransmitters
• make inside of cell more negative, moving the charge within the postsynaptic cell farther away from threshold
Neurotransmitters
- acetylcholine
- catecholamines
- norepinephrine
- epinephrine
- dopamine
- gamma-aminobutyric aid (GABA)
- glycine
Central Nervous system
- main components
- neuron cell bodies
- myelinated and unmyelinated nerve fibers
- glial cells
gray matter
• contains most of the neuron cell bodies
White matter
• contains most of the myelinated nerve fibers
Cerebrum
¥ largest part of brain in domestic animals
¥ functions associated with learning and intelligence
¥ surface covered with gyri separated by fissures and sulci
¥ longitudinal fissure divides into right and left cerebral hemispheres
• each hemisphere divided by sulci into lobes
• different lobes specialize in different functions
Cerebellum
¥ second largest component of the brain
¥ located caudal to the cerebrum
¥ area of brain responsible for coordinated movement, balance, posture, and complex reflexes
¥ damage or disease results in hypermetria
Diencephalon
- passageway between brain stem and cerebrum
- role in temperature regulation, hunger, thirst, and rage/anger responses
- associated structures
- thalamus
- hypothalamus
- pituitary
Brain stem
• connection between spinal cord and rest of the brain
• many cranial nerves originate here
• components
• medulla oblongata, the pons, and midbrain
• responsible for maintenance of basic support functions of the body – serious injury to this will almost always be fatal
- operates at subconscious level
Menings
¥ connective tissue layers that surround brain and spinal cord
¥ supply nutrients and oxygen, and provide some cushioning
¥ 3 layers
• dura mater (“tough mother”)
• Arachnoid (“spidery layer”)
• pia mater (“little mother”)
Cerebrospinal Fluid
CSF
¥ fluid between layers of meninges, and in canals and cavities inside brain and spinal cord
¥ provides cushioning function
¥ may play role in regulation of autonomic functions such as respiration and
vomiting
¥ CSF tap provides test sample for diagnosis of certain diseases or cancers
Blood-Brain Barrier
¥ separates capillaries in the brain from nervous tissue
• capillary walls in brain have no fenestrations
• covered by cell membranes of glial cells
¥ prevents many drugs, proteins, ions, and other molecules from readily passing from the blood into the brain – ** this will be very important to you as technicians when administering pre-anaesthetic sedatives, and induction drugs **
Cranial Nerves
- 12 pairs of nerves in PNS that originate directly from the brain
- numbered in Roman numerals from I through XII
- each nerve may contain
- axons of motor neurons
- axons of sensory neurons
- combinations of both
Spinal Cord
- caudal continuation of brain stem outside the skull
- lies in bony spinal canal formed by vertebrae
- conducts sensory information and motor instructions between brain and rest of the body
cortex
outer part of spinal cord
composed of white matter
surrounds the gray matter
Dorsal and Ventral Nerve Roots
roots emerge from each pair of adjacent vertebrae
dorsal nerve roots contain sensory (afferent) fibers
ventral nerve roots contain motor (efferent) fibers
(“in the back, out the belly”)
Autonomic Nervous System
controls automatic functions at the subconscious level
sympathetic nervous system
- thoracolumbar system
* nerves emerge from thoracic and lumbar vertebrae
parasympathetic nervous system
- cranial-sacral system
* nerves emerge from brain and sacral vertebral regions
