The Nervous System Flashcards
the nervous system and endocrine system coordinate
other organ systems to maintain homeostasis
the nervous system is
fast, short acting
the endocrine system is
slower, but longer lasting
the nervous system is
the most complex system in the body
functions of the nervous system
-monitors the body’s internal and external environments
-integrates sensory information
-coordinates voluntary and involuntary responses
anatomical divisions are
central nervous system (CNS) and peripheral nervous system (PNS)
central nervous system (CNS)
-made up of the brain and spinal cord
-integrates and coordinates input and output
peripheral nervous system (PNS)
-all the neural tissues outside of the CNS
-the connection between the CNS and the organs
functionals divisions are
afferent and efferent divisions
afferent division (in)
includes sensory receptors and neurons that send information to the CNS
efferent division (out)
includes neurons that send information to the effectors, which are the muscles and glands
efferent division divided into
somatic nervous system (SNS) and autonomic nervous system (ANS)
somatic nervous system (SNS)
controls skeletal muscle
autonomic nervous system (ANS)
controls smooth and cardiac muscle, and glands
two parts of autonomic nervous system
sympathetic and parasympathetic divison
neurons
-cells that communicate with one another and other cells
-have a very limited ability to regenerate when damaged or destroyed
basic structure of a neuron includes
-cell body
-dendrites
-axons
-axon terminals
dendrites
which receive signals
axons
which carry signals to the next cell
axon terminals
bulb-shaped ending that form a synapse with the next cell
cell bodies contains
-mitochondria, free and fixed ribosomes, and rough endoplasmic reticulum
-the axon hillock
-where electrical signal begins
structural classification of neurons
based on the relationship of the dendrites to the cell body
-multipolar, unipolar, bipolar neurons
multipolar neurons
are the most common in the CNS and have two or more dendrites and one axon
unipolar neurons
have the cell body off to one side, most abundant in the afferent division
bipolar neurons
have one dendrite and one axon with the cell body in the middle, and are rare (special senses)
sensory neurons also called
afferent neurons
sensory neurons
-total million or more
-receive information from sensory receptors
somatic sensory receptors
detect stimuli concerning the outside world, in the form of external receptors
-and our position in it, in the form of proprioceptors
visceral or internal receptors
monitor the internal organs
motor neurons also called
efferent neurons
motor neurons
-total about half a million in number
-carry information to peripheral targets called effectors
somatic motor neurons
innervate skeletal muscle
visceral motor neurons
innervate cardiac muscle, smooth muscle, and glands
interneurons (also called association neurons)
-by far the most numerous type at about 20 billion
-are located in the CNS
-function as links between sensory and motor processes
-have higher functions
-such as memory, planning, and learning
neuroglial cells
-are supportive cells and make up about half of all neural tissue
-four types are found in the CNS
-two types in the PNS
4 types of neuroglial cells in CNS
-astrocytes
-oligodendrocytes
-microglia
-ependymal cells
2 types of neuroglial in PNS
-satellite cells
-schwann cells
astrocytes
-large and numerous neuroglia in the CNS
-maintain the blood-brain barrier
oligodendrocytes
-produce an insulating membranous wrapping around axons called myelin
-small gaps between the wrapping called nodes of Ranvier
myelinated axons constitute the white matter of the CNS
-where cell bodies are grey matter
-some axons are unmyelinated
microglia
-the smallest and least numerous
-phagocytic cells derived from white blood cells
-perform essential protective functions such as engulfing pathogens and cellular waste
ependymal cells
-line the fluid-filled central canal of the spinal cord and the ventricles of the brain
-the endothelial lining is called the ependyma
-it is involved in producing and circulating cerebrospinal fluid around the CNS
satellite cells
-surround and support neuron cell bodies
-similar in function to the astrocytes in the CNS
schwann cells
-cover every axon in PNS
-the surface is the neurilemma
-produce myelin
organization of the nervous system in the PNS
-collections of nerve cell bodies are ganglia
-bundled axons are nerves
-including spinal nerves and cranial nerves
-can have both sensory and motor components
organization of the nervous system in the CNS
-collections of neuron cell bodies are found in centers, or nuclei
-neural cortex is a thick layer of gray matter
-white matter in the CNS is formed by bundles of axons called tracts, and in the spinal cord, form columns
-pathways are either sensory or ascending tracts, or motor or descending tracts
the membrane potential exists because of
-excessive positive ionic charges on the outside of the cell
-excessive negative charges on the inside, creating a polarized membrane
-an undisturbed cell has a resting membrane potential measured in the inside of the cell in millivolts
-the resting membrane potential of neurons in -70 mV
factors determining membrane potential
-extracellular fluid (ECF) is high in Na+
-intracellular fluid (ICF) is high in K+ and negatively charged proteins (Pr-)
-proteins are non-permeating, staying in the ICF
changes in membrane potential
-stimulus causes opening of Na+ channels
-opening of Na+ channels results in an influx of Na+
-moving the membrane toward 0 mV, a shift called
depolarization
-opening of K+ channels results in an efflux of K+
-moving the membrane further away from 0 mV, a shift
called hyperpolarization
-return to resting from depolarization: repolarizing
a change in the membrane that travels the entire length of neurons (action potentials)
a nerve impulse
if a combination of graded potentials causes the membrane to reach a critical point of depolarization, it is called the threshold (action potentials)
then an action potential will occcur
action potentials are
-all-or-none and will propagate down the length of the neuron
-from the time the voltage-gated channels open until repolarization is finished:
-the membrane cannot respond to further stimulation
-this period of time is the refractory period
-and limits the rate of response by neurons
propagation of an action potential
-occurs when local changes in the membrane in one site:
-result in the activation of voltage-gated channels in the
next adjacent site of the membrane
-this causes a wave of membrane potential changes
-continuous propagation
-occurs in unmyelinated fibers and is relatively slow
-saltatory propagation
-is in myelinated axons and is faster
the synapse
-a junction between a neuron and another cell
-occurs because of chemical messengers called neurotransmitters
-communication happens in one direction only
-between a neuron and another cell type is a neuroeffector junction
-such as the neuromuscular junction or neuroglandular junction
a synapse between two neurons occurs
-between the axon terminals of the presynaptic neuron
-across the synaptic cleft
-to the dendrite or cell body of the postsynaptic neuron
the synapse between two neurons neurotransmitters
-stored in vesicles of the axon terminals
-released into the cleft and bind to receptors on the postsynaptic membrane
important neurotransmitters
-acetylcholine (ACh)
-norepinephrine (NE)
-dopamine, GABA, and serotonin
-at least 50 less-understood neurotransmitters
-NO and CO
norepinephrine (NE)
in the brain and part of the ANS
dopamine, GABA, and serotonin
are CNS neurotransmitter(only in the CNS)
NO and CO
are gases that act as neurotransmitters
usually, ACh and NE trigger depolarization
-an excitatory response
-with the potential of reaching threshold
usually, dopamine, GABA, and serotonin trigger hyperpolarization
-an inhibitory response
-making it farther from threshold
neuronal pools
multiple presynaptic neurons can synapse with one postsynaptic neuron
if they all release excitatory neurotransmitters
then an action potential can be triggered
if they all release an inhibitory neurotransmitter
then no action potential can occur
if half release excitatory and half inhibitory neurotransmitters
they cancel, resulting in no action
neuronal pools is a
term that describes the complex grouping of neural pathway or circuits
divergence
is a pathway that spreads information from one neuron to multiple neurons
convergence
is when several neurons synapse with a single postsynaptic neuron
divergence (1 to 2 to 3)
a mechanism for spreading stimulation to multiple neurons or neuronal pools in the CNS
convergence (4 to 1)
a mechanism for providing input to a single neuron from multiple sources
the meninges
the neural tissue in the CNS is protected by three layers of specialized membranes
levels of meninges
- dura mater
- arachnoid mater
-subarachnoid space - pia mater
spinal cord structure
the major neural pathway between the brain and the PNS
can also act as an integrator in the spinal reflexes
-31 pairs of spinal nerves in humans
consistent in diameter excerpt for the cervical enlargement and lumbar enlargement
-where numerous nerves supply upper and lower limbs
central canal
-a narrow passage containing cerebrospinal fluid
spinal segments are identified by
a letter and number relating to the nearly vertebrae (eg C5, T3, L1)
spinal segemnts
each has a pair of dorsal root ganglia
-containing the cell bodies of sensory neurons with axons in dorsal root
ventral roots contain motor neuron axons
-roots are contained in one spinal nerve
sectional anatomy of spinal cord
the central gray matter is made up of glial cells and nerve cell bodies
projections of gray matter are called horns
-which extend out into the white matter
white matter is myelinated and unmyelinated axons
the location of cell bodies in specific nuclei of gray matter relate to their function
white matter can be organized into three columns
-which contain either ascending tracts to the brain, or descending tracts from the brain to the PNS
six major regions of the brain
cerebrum, diencephalon, midbrain, pons, medulla oblongata, and cerebellum
the cerebrum
is divided into two paired cerebral hemispheres
deep to the cerebrum is the diencephalon
which is divided into the epithalamus, thalamus and hypothalamus
the brain stem
contains the midbrain, pons, and medulla oblongata
the cerebellum
is the most inferior/posterior part
the ventricles of the brain
filled with cerebrospinal fluid and lined with ependymal cells
filled with cerebrospinal fluid and lined with ependymal cells
the two lateral ventricles within each cerebral hemisphere drain through the:
interventricular foramen into the:
third ventricle in the diencephalon, which drains through the cerebral aqueduct into the:
fourth ventricle, which drains into the central canal
Cerebrospinal fluid (CSF)
-surrounds and bathes the exposed surfaces of the CNS
-transport nutrients, chemicals, and wastes
-is produced by the choroid plexus
-continually secreted and replaced
the cerebrum
contains an outer gray matter called the cerebral cortex
-deep gray matter in the cerebral nuclei and white matter of myelinated axons beneath the cortex and around the nuclei
the surface of the cerebrum
-folds into gyri
-separated by depressions called sulci or deeper grooves called fissures
the cerebral hemispheres includes
temporal lobe, parietal lobe, occipital lobe
the temporal lobe
-inferior to the lateral sulcus
-overlaps the insula
the parietal lobe
-extends between the central sulcus and the parieto-occipital sulcus
the occipital lobe
located mostly posteriorly
the cerebral hemispheres
the lobes are named from the cranial bone above it
each lobe has sensory regions and motor regions
each hemisphere sends and receives information from the opposite side of the body
motor and sensory areas of the cortex
are divided by the central sulcus
the precentral gyrus of the frontal lobe
-contains the primary motor cortex
the postcentral gyrus of the parietal lobe
-contains the primary sensory cortex
the visual cortex is in the occipital lobe
the gustatory, auditory, and olfactory cortexes are in the temporal lobe
association areas
interpret incoming information
coordinate a motor response, integrating the sensory and motor cortexes
the somatic sensory association are
-helps to recognize touch
the somatic motor association area
-is responsible for coordinating movement
cortical connections
regions of the cortex are linked by the deeper white matter
the left and right hemispheres are linked across the corpus callosum
other axons link the cortex with:
-the diencephalon, brain stem, cerebellum, and spinal cord
higher-order centers
integrative areas, usually only in the left hemisphere
the general interpretive area or Wernicke’s area
-integrates sensory information to form visual and auditory memory
the speech center or Broca’s area
-regulates breathing and vocalization, the motor skills needed for speaking
the prefrontal cortex
in the frontal lobe
coordinates information from the entire cortex
skills such as (the prefrontal cortex)
-predicting time lines
-making judgements
feelings such as (the prefrontal cortex)
frustration, tension, and anxiety
hemispheric lateralization
the concept that different brain functions can and do occur on one side of the brain
present in humans as well as nonhuman animals
the left hemisphere
tends to be involved in language skills, analytical tasks, and logic
the right hemisphere
tends to be involved in analyzing sensory input and relating it to the body, as well as analyzing emotional content
fact memory
the recall of bits of information
skill memory
learned motor skill that can become incorporated into unconscious memory
short-term memory
doesn’t last long unless rehearsed
converting into long-term memory through consolidation
long-term memory
remains for long periods, sometimes an entire lifetime
amnesia
memory loss as result of disease or trauma
the limbic system
-includes the olfactory cortex, basal nuclei, gyri, and tracts between the cerebrum and diencephalon
-a functional grouping, rather than an anatomical one
-establishes the emotional states
-links the conscious with the unconscious
-aids in long-term memory with help of the hippocampus
the diencephalon
-contains switching and relay centers
-centers integrate conscious and unconscious sensory information and motor commands
-surround third ventricle
three components in the diencephalon
epithalamus, thalamus, and hypothalamus
the epithalamus
-lies superior to the third ventricle and forms the roof of the diencephalon
-the anterior part contains choroid plexus
-the posterior part contains the pineal gland that is endocrine and secretes melatonin
the thalamus
-the left and right thalamus are separated by the third ventricle
-the final relay point for sensory information
-only a small part of this input is sent on to the primary sensory cortex
the hypothalamus
-lies inferior to the third ventricle
-the subconscious control of skeletal muscle contraction is associated with strong emotion
-adjusts the pons and medulla functions
-coordinates the nervous and endocrine systems
-secretes hormones
produces sensations of thirst and hunger
-coordinates voluntary and ANS function
-regulates body temperature
-coordinates daily cycles
reticular formation found in the midbrain
is a network of nuclei related to the state of wakefulness
pons control
basal breathing rate and depth
the medulla oblongata
-connects the brain with the spinal cord
-contains reflex centers
cardiovascular centers
adjust heart rate and arteriolar diameter
respiratory rhythmicity centers
regulate respiratory rate
visceral reflexes
maintain a balance of function in the organ systems of the body
the cerebellum
An automatic processing center
-Which adjusts postural muscles to maintain balance
Programs and fine-tunes movements
The cerebellar peduncles
-Are tracts that link the cerebral cortex, basal nuclei, and brain stem
Ataxia
-Is disturbance of coordination
-Can be caused by damage to the cerebellum
peripheral nervous system
-links the CNS to the rest of the body through peripheral nerves
-they include the cranial nerves and the spinal nerves
-the cell bodies of sensory and motor neurons are contained in the ganglia
the crainal nerves
12 pairs, notes as Roman numerals I through XII
Some are:
-only motor pathways
-only sensory pathways
-mixed, having both sensory and motor neurons
the olfactory nerves (N I)
-are connected to the cerebrum
-carry information concerning the sense of smell
the optic nerves (N II)
-carry visual information from the eyes, through the optic foramina of the orbits to the optic chiasm
-continue as the optic tracts to the nuclei of the thalamus
the oculomotor nerves (N III)
-motor only, arising in the midbrain
-innervate four of six extrinsic eye muscles and the intrinsic eye muscles that control the size of the pupil
the trochlear nerves (N IV)
-smallest, also arise in the midbrain
-innervate the superior oblique extrinsic muscles of the eyes
the trigeminal nerves (N V)
-have nuclei in the pons, are the largest cranial nerves
-have three branches
the abducens nerves (N VI)
-innervate only the lateral rectus extrinsic eye muscle, with the nucleus in the pons
the facial nerves (N VII)
-Mixed, and emerge from the pons
-Sensory fibers monitor proprioception in the face
-Motor fibers provide facial expressions; control tear and salivary glands
The vestibulocochlear nerves (N VIII)
-respond to sensory receptors in the inner ear
the glossopharyngeal nerves (N IX)
-Mixed nerves innervating the tongue and pharynx
-Their nuclei are in the medulla oblongata
-The sensory portion monitors taste on the posterior third of the tongue and monitors BP and blood gases
-The motor portion controls pharyngeal muscles used in swallowing, and fibers to salivary glands
the vagus nerves (N X)
-Have sensory input vital to autonomic control of the viscera
-Motor control includes the soft palate, pharynx, and esophagus
-Are a major pathway for ANS output to cardiac muscle, smooth muscle, and digestive glands
the accessory nerves (N XI)
the accessory nerves (N XI)
-Have fibers that originate in the medulla oblongata
-Also in the lateral gray horns of the first five cervical segments of the spinal cord
the hypoglossal nerves (N XII)
-provide voluntary motor control over the tongue
the spinal nerves
-Found in pairs grouped according to the region of the vertebral column
-Thirty-one pairs in humans:
-8 pairs of cervical nerves, C1–C8
-12 pairs of thoracic nerves, T1–T12
-5 pairs of lumbar nerves, L1–L5
-5 pairs of sacral nerves, S1–S5
-1 pair of coccygeal nerves, Co1
dermatome
a clinically important area monitored by a specific spinal nerve
reflexes
-rapid, autonomic, unlearned motor response to a stimulus
-usually removes or opposes the original stimulus
-monosynaptic reflexes
monosynaptic reflexes example
for example, the stretch reflex
-the simplest, with only one synapse
-the best known stretch reflex is probably the knee-jerk reflex
types of complex reflexes
polysynaptic reflexes, withdrawal reflexes, reciprocal inhibition
polysynaptic reflexes
-with at least one interneuron
-are slower than monosynaptic reflexes, but can activate more than one effector
withdrawal reflexes
-like the flexor reflex, move a body part away from the stimulation
-like touching a hot stove
reciprocal inhibition
-blocks the flexor’s antagonist
-to ensure that flexion is in no way interfered with
the autonomic nervous system
-Unconscious adjustment of homeostatically essential visceral responses
-Sympathetic division
-Parasympathetic division
-The somatic NS and ANS are anatomically different
-SNS: one neuron to skeletal muscle
-ANS: two neurons to cardiac and smooth muscle, glands, and fat cells
the sympathetic divison (also called the “fight-or-flight” division)
Effects
-Increase in alertness, metabolic rate, sweating, heart rate, blood flow to skeletal muscle
-Dilates the respiratory bronchioles and the pupils
-Blood flow to the digestive organs is decreased
-E and NE from the adrenal medullae support and prolong the effect
the parasympathetic division (also called “rest-and-digest” division)
Effect
-Constriction of the pupils, increase in digestive secretions, increase in digestive tract smooth muscle activity
-Stimulates urination and defecation
-Constricts bronchioles, decreases heart rate
dual innervation
-Refers to both divisions affecting the same organs
-Mostly have antagonistic effects
-Some organs are innervated by only one division
aging and the nervous system
Common changes
-Reduction in brain size and weight and reduction in number of neurons
-Reduction in blood flow to the brain
-Change in synaptic organization of the brain
-Increase in intracellular deposits and extracellular plaques
-Senility can be a result of all these changes
