chapter 8 the nervous system Flashcards
What are the functions of the nervous system?
detect changes and feel sensations
initiate responses to changes
organize information and store it
what does the nervous system consist of?
the CNS- brain and spinal cord
the PNS- cranial and spinal nerves and the ANS
What are nerve cells called?
neurons or nerve fibers
What are dendrite cells?
conduct nerve impulses towards the cell body
neurons may have hundreds of dendrites
What are Axons?
conduct nerve impulses away from the cell body
Neurons only have one axon
Where are neuron cell bodies found?
in the CNS
What kind of cells are found in the CNS?
Oligodendrocytes and microglia
What kind of cells are found in the PNS
schwann cells and myelin sheath
What are schwann cells?
consists of axons and dendrites
grow to surround the neuron processes, enclosing them in layers of Schwann cell membrane
produce myelin sheath around axons
What is the myelin sheath?
a phospholipid that electrically insulated neurons from one to another
What are the nodes of Ranvier?
spaces between adjacent Schwann cells or segments of the myelin sheath
What is the function of the Nodes of Ranvier?
parts of the neuron cell membrane that depolarize when an electrical impulse is transmitted
What is the neurolemma?
the nuclei and cytoplasm of the Schwann cells are wrapped around the outside of the myelin sheath
What is the function of neurolemmas?
essential for the regeneration of neurons
What are oligodendrocytes?
produce myelin sheaths around axons of the CNS
one of the neuroglia
Why doesn’t the regeneration of neurons happen in the CNS?
There are no Schwann cells present which means there is no neurolemma
This is why severing of the spinal cord results in permanent loss of function
What are the microglia?
another kind of neuroglia
they are phagocytes- they clean up cellular debris and damaged cells and phagocytize pathogens
What are asrocytes?
another kind of neuroglia
they provide framework for the migrating neurons that will form the brain
help regulated localized blood flow within the brain
What do Astrocytes contribute to?
Blood-Brain Barrier- which prevents potentially harmful waste products in the blood from diffusing out into brain tissue
What are disadvantages of the blood-brain barrier?
some useful medications cannot cross it
antibodies produced by lymphocytes cross only with difficulty
What is Polarization?
a neuron not carrying an impulse
more Na+ ions outside cell/ more K+ ions and negative ions inside the cell
results in positive charge outside of cell membrane and negative charge inside cell
What is depolarization
entry on na+ ions
reversal of charges on either side of the membrane
outside now has a negative charge and inside has positive charge
What is repolarization?
K+ ions exit the cell
this restores positive charge outside and the negative inside
What does the term action potential refer to?
depolarization followed by repolarization
What do the sodium and potassium pumps do?
they return Na+ ions outside and K+ ions inside
the neuron is now ready to respond to another stimulus and transmit another impulse
What is saltatory conduction?
in a myelinated neuron only the nodes of Ranvier depolarize
increase speed of impulses
How do nerve impulses differ?
they are all exactly the same but they different effects depending on on their various destinations
(muscles,glands, or other neurons)
What is a nerve impulse considered as?
like a switch or signal that activates the cell, tissue, or organ of its destination
What is the synapse?
the small gap between the axon of one neuron and the dendrites or cell body of the next neuron
What happens during the process of a synapse?
A neurotransmitter carries the impulse across a synapse and is then destroyed by a chemical inactivator or absorbed
Many synapses are termed excitatory why?
the neurotransmitter causes the postsynaptic neuron to depolarize
transmits an electrical pulse
Why are some synapses termed inhibitory?
the neurotransmitter causes the postsynaptic neuron to hyperpolarize
What is hyperpolarization?
the neuron membrane becomes even more positive outside as K+ ions leave the cell or Cl- ions enter the cell
does not transmit an electrical impulse
What groups are neurons classified as?
Sensory neurons, motor neurons, and interneurons
What are sensory neurons?
carry impulses from receptors to the CNS
may be somatic (from skin, skeletal muscles, joints)
or visceral (from internal organs)
What are receptors?
structures that detect external or internal changes and generate impulses that travel along afferent neurons to the CNS
Sensory neurons from receptors in skin, skeletal muscles and joints are called?
somatic
Sensory neurons from receptors in internal organs are called?
visceral sensory neurons
What are motor neurons (efferent neurons)?
carry impulses from the CNS to effectors
may be somatic (to skeletal muscle)
or visceral (to smooth muscle, cardiac muscle, or glands)
What are the two general type of effectors?
muscles-contract or relax
glands-secrete or do not
Sensory and motor neurons make up what system?
The PNS
Visceral motor neurons make up what system?
Autonomic nervous system (ANS)
What are interneurons?
carry only sensory or motor impulses, or to integrate these functions
found entirely within the CNS
some interneurons are concerned with thinking, learning and memory
What is a nerve?
a group of axons and/ or dendrites of many neurons, with blood vessels and connective tissue
What are sensory nerves?
are made only of sensory neurons
ex: optic nerves-vision
olfactory nerves-smell
What are motor nerves?
made only of motor neurons
autonomic neurons are motor nerves
What is a mixed nerve?
contains both sensory and motor neurons
Ex: peripheral nerves
What is a nerve tract?
groups of neurons within the CNS
aka white matter
What is the function of the spinal cord?
transmits impulses to and from the brain, and integrates the spinal cord reflexes
Location of the spinal cord?
within the vertebral canal
extends from the foramen magnum to the disc between the 1st and 2nd lumber vertebra
What is the H- shaped gray matter of the spinal cord?
contains cell bodies of motor neurons and interneurons
What is the external white matter of the spinal cord?
myelinated axons and dendrites of interneurons
What do the ascending tracts do?
carry sensory impulses to the brain
What do the descending tracts do?
carry motor impulses away from the brain
What is within the central canal?
cerebrospinal fluid and is continuous with the ventricles of the brain
How many pairs of spinal nerves?
31 pairs
8 cervical pairs
12 thoracic pairs
5 lumbar pairs
5 sacral pairs
1 small coccygeal pair
What is the cauda equina?
the lumbar and sacral nerves that extend below the end of the spinal cord
What does each spinal nerve have?
two roots: neurons entering or leaving the spinal cord
What is the dorsal root?
is made of sensory neurons that carry impulses into the spinal cord
What is the dorsal root ganglion?
an enlarged part of the dorsal root that contains the cell bodies of the sensory neurons
What is the ventral root?
the motor root
made of the axons of motor neurons carrying impulses from the spinal cord to muscles or glands
What is a reflex?
involuntary response to a stimulus, automatic action
What is the reflex arc?
pathway that nerve impulses travel when a reflex is elicited
What does the reflex arc consist of?
1.Receptors
2.Sensory neurons
3.Central nervous system
4.Motor neurons
5.Effector
What is the stretch reflex?
a muscle that is stretched will contract
patellar reflex is used clinically to determine whether the nervous system is functioning properly
What are flexor reflexes (withdrawal reflexes)
a painful stimulus will cause withdrawal of the body part
What are the ventricles of the brain?
four cavities: two lateral ventricles , the third ventricle, the fourth ventricle
each contains a choroid plexus that forms cerebrospinal fluid
What is the function of the medulla?
regulates the vital functions of heart rate, breathing, and blood pressure
regulates reflexes of coughing, sneezing, swallowing and vomiting
What are within the pons?
respiratory centers that work with those in the medulla
What is within the midbrain?
centers for visual reflexes, auditory reflexes, and righting (equilibrium) reflexes
What is the function of the cerebellum?
regulates coordination of voluntary movement, muscle tone, stopping movements and equilibrium
contributes to sensations involving texture and weight
What are the functions of the hypothalamus?
-produces ADH
-produces oxycotin
-produces releasing hormones
-regulated body temp
-regulates food intake
-integrates the functioning of the ANS
-regulates body rhythms
What are the functions of the thalamus?
-groups sensory impulses as to body part before relaying them to the cerebrum
-awareness of pain but inability to localize
-suppresses unimportant sensations to permit concentration
-contributes to alertness and awareness and to memory
What is the the cerebrum?
largest part of the brain
consists of two hemispheres separated by the longitudinal fissure
what is the corpus callosum?
a band of 200 million neurons that connects the right and left hemispheres of the cerebrum
What is the cerebral cortex?
the surface grey matter of cerebrum which consists of cell bodies of neurons and is folded extensively into convulsions
What is the internal white matter of the cerebrum?
consists of nerve tracts that connect the lobes of the cerebrum to another and other parts of the brain
What is within the frontal lobes?
motor areas-initiate voluntary movement
premotor area- regulates sequence of movements for learned skills
prefrontal area- for aspects of social behavior
broca’s motor speech area- regulates the movements involved in speech
What is within the parietal lobes?
general sensory area- feels and interprets the cutaneous senses and conscious muscle sense
taste area- extends into temporal lobe, for sense of taste
speech areas- (left hemisphere) for thought before speech
What is within the temporal lobes?
auditory areas- for hearing and interpretation
olfactory areas- for sense of smell and interpretation
speech areas- for thought before speech
what is within the occipital lobes?
visual areas-for vision
interpretations areas- for spatial relationships
what is within the association areas?
in all lobes for abstract thinking, reasoning, learning, memory, and personality.
The hipocampi are essential for the formation of memories
neural plasticity- the ability of the brain to adapt to changing needs
What is the basal ganglia?
small masses of gray matter within the cerebral hemispheres
regulate accessory movements such as gestures and facial expressions as well as muscle tone
What are meninges?
the connective tissue membranes that cover the brain and spinal cord
three layers
What are the three layers of meninges?
outermost layer- dura matter; lines the skull an vertebral canal
middle layer- arachnoid membrane web like strands of connective tissue
inner layer- pia matter’ on surface of the spinal cord and brain
What is the subarachnoid space?
between the arachnoid and pia matter that contains cerebrospinal fluid
How is cerebrospinal fluid (CSF) formed?
formed continuously in the ventricles of the brain by choroid plexus, from blood plasma
How does CSF circulate?
from the ventricles to the central canal of the spinal cord and to the cranial and spinal subarachnoid spaces
How is CSF reabsorbed?
from the cranial subarachnoid space through arachnoid villi into the blood in the cranial venous sinuses
rate of reabsorption equals the rate of production
How does CSF contribute to the CNS?
as tissue fluid, it brings nutrients to the CNS neurons and remove wastes products.
CSF also acts a shock absorber to cushion the CNS
Function of the cranial nerves?
concerned with vision, hearing and equilibrium, taste and smell and man other functions within the head and viscera
What is the Autonomic nervous system?
part of the PNS
consists of motor neurons to visceral effectors
has two divisions sympathetic and parasympathetic
What does an ANS pathway consist of?
two neurons that synapse in a ganglion
preganglionic neurons- from the CNS to the ganglia
postganglionic neurons- from the ganglia to the effectors
Sympathetic division
most sympathetic ganglia are in two chains just outside the vertebral column
dominates during stressful situations;responses prepare the body to meet physical demands
parasympathetic division
parasympathetic ganglia are very near or in the visceral effectors
dominates in relaxed situations to permit normal functioning
What is Acetlychloline?
the transmitter released by all preganglionic neurons both sympathetic and parasympathetic
inactivator is cholinesterase
What do sympathetic postganglionic neurons release?
norepinephrine
inactivator is catechol-o-methyl transferase (COMT) or monoamine oxidase (MAO)
