201 Flashcards
Central Nervous System (CNS)
consists of the brain and spinal cord
The peripheral nervous system (PNS)
consists of all nervous tissue outside the CNS. Components of the PNS include nerves and sensory receptors.
Nervous system divisions
- Nervous system is dived into CNS and PNS
- CNS receives input for the sensory branch of the PNS, interprets is and then out puts signals to the motor brand of the PNS
PNS divisions
- is divided into Sensory and Motor divisions
- Motor division is dived into somatic and autonomic
- autonomic is dived into sympathetic and parasympathetic
The PNS is divided into a sensory (afferent) division and a motor (efferent) division.
- The sensory division conveys sensory input into the CNS from sensory receptors.
- The motor division conveys motor output from the CNS to effectors (muscles and glands).
The efferent (motor) division of the PNS is further subdivided into a somatic nervous system and an autonomic nervous system.
- somatic nervous system (conveys motor output from the CNS to skeletal muscles only)
- autonomic nervous system (conveys motor output from the CNS to smooth muscle, cardiac muscle, and glands).
The autonomic nervous system in turn is divided into a sympathetic division, parasympathetic division, and enteric plexuses.
The enteric plexuses in the wall of the digestive canal regulate the smooth muscle and glands of the digestive canal
The nervous system helps maintain homeostasis and integrates all body activities.
it does this by sensing changes (sensory function), interpreting them (integrative function), and reacting to them (motor function).
Nervous tissue consists of
neurons (nerve cells) and neuroglia.
Neurons have the property of electrical excitability
and are responsible for most unique functions of the nervous system: sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions.
Most neurons have three parts.
1-The dendrites are the main receiving or input region
2-The cell body, Integration occurs in the cell body, which includes typical cellular organelles.
3-the Axon, responsible for output which propagates nerve impulses toward another neuron, a muscle fiber, or a gland cell.
Synapses
the site of functional contact between two excitable cells. Axon terminals contain synaptic vesicles filled with neurotransmitter molecules.
slow axonal transport and fast axonal transport
systems for conveying materials to and from the cell body and axon terminals.
On the basis of their structure, neurons are classified as
- multipolar,
- bipolar,
- unipolar or pseudounipolar.
Neurons are functionally classified as
- sensory (afferent) neurons,
- motor (efferent) neurons,
- interneurons
Sensory neurons carry sensory information into the CNS.
Motor neurons carry information out of the CNS to effectors (muscles and glands).
Interneurons
located within the CNS between sensory and motor neurons.
Neuroglia
support, nurture, and protect neurons and maintain the interstitial fluid that bathes them.
Neuroglia in the CNS consist of
- astrocytes
- oligodendrocytes
- microglial cells
- ependymal cells
Neuroglia in the PNS consist of
- Schwann cells
- satellite cells.
Two types of neuroglia produce myelin sheaths:
Oligodendrocytes myelinate axons in the CNS, and Schwann cells myelinate axons in the PNS.
White matter consists of aggregates of myelinated axons
gray matter contains cell bodies, dendrites, and axon terminals of neurons unmyelinated axons, and neuroglia.
In the spinal cord, gray matter forms an H-shaped inner core that is surrounded by white matter.
In the brain, a thin, superficial shell of gray matter covers the cerebral and cerebellar hemispheres
Neurons communicate with one another
- using graded potentials, which are used for short-distance communication only
- nerve impulses, which allow communication over long distances within the body.
The electrical signals produced by neurons and muscle fibers rely on four kinds of ion channels:
- leak channels
- ligand-gated channels
- mechanically gated channels
- voltage-gated channels.
Leak channels
- Gated channels that randomly open and close.
- Found in nearly all cells, and dendrites, cell bodies, and axons of all types of neurons.
Ligand-gated channels Gated channels
- open in response to binding of ligand (chemical) stimulus.
- found on dendrites of some sensory neurons such as pain receptors and dendrites and cell bodies of interneurons and motor neurons.
Mechanically gated channels
- open in response to mechanical stimulus (such as touch, pressure, vibration, or tissue stretching).
- found on Dendrites of some sensory neurons such as touch receptors, pressure receptors, and some pain receptors.
Large nerve fibers
transmit impulses faster than small ones do
Which of the following cell types can conduct action potentials?
1) smooth muscle cells
2) cardiac muscle cells
3) neurons
4) neuroglia
5) skeletal muscle cells
all the above
Which of the following cell types can produce action potentials when stimulated?
1) smooth muscle cells
2) cardiac muscle cells
3) neurons
4) neuroglia
5) skeletal muscle cells
1,2,3,5
Which one of the following is NOT found in the central nervous system?
a. myelinated fibers
b. unmyelinated fibers
c. neurolemma
d. oligodendrocytes
e. astrocytes
C neurolemma is not part of the CNS
How is the resting membrane potential of -70mv (millivolts) best interpreted?
the inside of the fiber is 70mv more negative than the outside
The sodium pump:
actively transports sodium out of the cell
During the absolute refractory period a second action potential response can be produced:
never
A large number of nerve fibers running together within the central nervous system is referred to as a:
tract
gray matter contains mostly
neuron cell bodies and synapses
Cerebrospinal fluid is found between the:
pia and archnoid
Transmission across a chemical synapse is always in the same direction
true
A spinal puncture places the needle tip in the:
subarchnoid space
The anterior gray columns contain:
cell bodies of motor neurons
: reflex arc
is the simplest unit capable of detecting a stimulus and causing a response
The vital centers for control of heart, respiration and blood pressure are located in the:
medulla oblongata
The major control systems for balance and posture in the body as well as muscular coordination are located in the:
cerebellum
The most important central mechanism for temperature regulation is contained in the:
hypothalamus
corpus callosum
is the nerve fibers that connect the Hemispheres of the cerebrum
A resting membrane potential exists across the plasma membrane of excitable cells that are unstimulated (at rest).
The resting membrane potential exists because of a small buildup of negative ions in the cytosol along the inside surface of the membrane, and an equal buildup of positive ions in the extracellular fluid along the outside surface of the membrane.
A typical value for the resting membrane potential of a neuron is −70 mV.
A cell that exhibits a membrane potential is polarized.
The resting membrane potential is determined by three major factors:
(1) unequal distribution of ions in the ECF and cytosol;
(2) inability of most cytosolic anions to leave the cell;
(3) electrogenic nature of the Na+/K+ ATPases.
Graded Potentials
- A graded potential is a small deviation from the resting membrane potential that occurs because ligand-gated or mechanically gated channels open or close.
- A hyperpolarizing graded potential makes the membrane potential more negative (more polarized).
- A depolarizing graded potential makes the membrane potential less negative (less polarized).
- The amplitude of a graded potential varies, depending on the strength of the stimulus.
Action Potentials all-or-none principle
- if a stimulus is strong enough to generate an action potential, the impulse generated is of a constant size.
- A stronger stimulus does not generate a larger action potential.
- Instead, the greater the stimulus strength above threshold, the greater the frequency of the action potentials.
During an action potential, voltage-gated Na+ and K+ channels open and close in sequence.
This results first in depolarization, the reversal of membrane polarization (from −70 mV to +30 mV). Then repolarization, the recovery of the resting membrane potential (from +30 mV to −70 mV), occurs.
During the first part of the refractory period (RP), another action potential cannot be generated at all (absolute RP);
a little later, it can be triggered only by a larger-than-normal stimulus (relative RP).
an action potential travels from point to point along the membrane without getting smaller,
it is useful for long-distance communication
Nerve impulse propagation in which the impulse “leaps” from one myelin sheath gap to the next along a myelinated axon is saltatory conduction
. Saltatory conduction is faster than continuous conduction.
Axons with larger diameters conduct nerve impulses at higher speeds than do axons with smaller diameters.
The intensity of a stimulus is encoded in the frequency of nerve impulses and in the number of sensory neurons that are recruited.
A synapse is the functional junction between one neuron and another, or between a neuron and an effector such as a muscle or a gland.
The two types of synapses are electrical and chemical.
A chemical synapse produces one-way information transfer—
from a presynaptic neuron to a postsynaptic neuron.
An excitatory neurotransmitter is one that can depolarize the postsynaptic neuron’s membrane, bringing the membrane potential closer to threshold.
An inhibitory neurotransmitter hyperpolarizes the membrane of the postsynaptic neuron, moving it further from threshold.
hyperpolarized = more negavite
depolarized = less negative
There are two major types of neurotransmitter receptors:
ionotropic receptors and metabotropic receptors.
ionotropic receptor contains a neurotransmitter binding site and an ion channel.
A metabotropic receptor contains a neurotransmitter binding site and is coupled to a separate ion channel by a G protein
Neurotransmitter is removed from the synaptic cleft in three ways:
diffusion, enzymatic degradation, and uptake by cells (neurons and neuroglia
If several presynaptic end bulbs release their neurotransmitter at about the same time
, the combined effect may generate a nerve impulse, due to summation. Summation may be spatial or temporal
The postsynaptic neuron is an integrator.
It receives excitatory and inhibitory signals, integrates them, and then responds accordingly.
Both excitatory and inhibitory neurotransmitters are present in the CNS and the PNS.
A given neurotransmitter may be excitatory in some locations and inhibitory in others
Neurotransmitters can be divided into two classes based on size: (1) small-molecule neurotransmitters (acetylcholine, amino acids, biogenic amines, ATP and other purines, nitric oxide, and carbon monoxide), and (2) neuropeptides, which are composed of 3 to 40 amino acids.
(1) small-molecule neurotransmitters (acetylcholine, amino acids, biogenic amines, ATP and other purines, nitric oxide, and carbon monoxide), and
(2) neuropeptides, which are composed of 3 to 40 amino acids.
Neurons in the central nervous system are organized into networks called neural circuits.
Neural circuits include simple series, diverging, converging, reverberating, and parallel after-discharge circuits.
The nervous system exhibits plasticity (the capability to change based on experience)
it has very limited powers of regeneration (the capability to replicate or repair damaged neurons).
Neurogenesis, the birth of new neurons from undifferentiated stem cells, is normally very limited. Repair of damaged axons does not occur in most regions of the CNS.
Axons and dendrites that are associated with a neurolemma in the PNS may undergo repair if the cell body is intact, the Schwann cells are functional, and scar tissue formation does not occur too rapidly
The spinal cord is protected by
- vertebral column,
- meninges,
- cerebrospinal fluid,
- denticulate ligaments
The three meninges are coverings that run continuously around the spinal cord and brain.
They are the
- dura mater
- arachnoid mater
- pia mater.
The spinal cord begins as a continuation of the medulla oblongata and ends at about the second lumbar vertebra in an adult.
The spinal cord contains cervical and lumbosacral enlargements that serve as points of origin for nerves to the limbs
The tapered inferior portion of the spinal cord is the conus medullaris
from which arise the filum terminale and cauda equina
Spinal nerves connect to each segment of the spinal cord by two roots.
- the posterior root contains sensory axons
- the anterior root contains motor neuron axons.
The anterior median fissure and the posterior median sulcus
partially divide the spinal cord into right and left sides.
The gray matter in the spinal cord is divided into horns, and the white matter into funiculi.
In the center of the spinal cord is the central canal, which runs the length of the spinal cord
Parts of the spinal cord observed in transverse section are the gray commissure; central canal; anterior, posterior, and lateral gray horns; and anterior, posterior, and lateral white funiculi, which contain ascending and descending tracts. Each part has specific functions
gray commissure; central canal; anterior, posterior, and lateral gray horns; and anterior, posterior, and lateral white funiculi, which contain ascending and descending tracts. Each part has specific functions
The 31 pairs of spinal nerves are named and numbered according to the region and level of the spinal cord from which they emerge. There are 8 pairs of cervical, 12 pairs of thoracic, 5 pairs of lumbar, 5 pairs of sacral, and 1 pair of coccygeal nerves.
- 8 pairs of cervical
- 12 pairs of thoracic
- 5 pairs of lumbar
- 5 pairs of sacral
- 1 pair of coccygeal nerves
Spinal nerves typically are connected with the spinal cord by a posterior root and an anterior root.
All spinal nerves contain both sensory and motor axons (they are mixed nerves).
Three connective tissue coverings associated with spinal nerves are the endoneurium, perineurium, and epineurium.
endoneurium, perineurium, and epineurium.
. Branches of a spinal nerve include the posterior ramus, anterior ramus, meningeal branch, and communicating rami.
The anterior rami of spinal nerves, except for T2–T12, form networks of nerves called plexuses.
Anterior rami of nerves T2–T12 do not form plexuses and are called intercostal nerves.
They are distributed directly to the structures they supply in intercostal spaces.
dermatomes
Sensory neurons within spinal nerves serve specific, constant segments of the skin
Cervical Plexus
- The cervical plexus is formed by the roots (anterior rami) of the first four cervical nerves (C1–C4), with contributions from C5.
- Nerves of the cervical plexus supply the skin and muscles of the head, neck, and upper part of the shoulders; they connect with some cranial nerves and innervate the diaphragm.
Brachial Plexus
- The roots (anterior rami) of spinal nerves C5–C8 and T1 form the brachial plexus.
- Nerves of the brachial plexus supply the upper limbs and several neck and shoulder muscles.
Lumbar Plexus
- The roots (anterior rami) of spinal nerves L1–L4 form the lumbar plexus.
- Nerves of the lumbar plexus supply the anterolateral abdominal wall, external genitals, and part of the lower limbs.
Sacral and Coccygeal Plexuses
- The roots (anterior rami) of spinal nerves L1–L5 and S1–S4 form the sacral plexus.
- Nerves of the sacral plexus supply the buttocks, perineum, and part of the lower limbs.
- The roots (anterior rami) of the spinal nerves S4–S5 and the coccygeal nerves form the coccygeal plexus.
- Nerves of the coccygeal plexus supply the skin of the coccygeal region.
Spinal Cord Physiology
- The white matter tracts in the spinal cord are highways for nerve impulse propagation. Along these tracts, sensory input travels toward the brain, and motor output travels from the brain toward skeletal muscles and other effector tissues. Sensory input travels along two main routes in the white matter of the spinal cord: the posterior funiculi and the spinothalamic tract. Motor output travels along two main routes in the white matter of the spinal cord: direct pathways and indirect pathways.
A second major function of the spinal cord is to serve as an integrating center for spinal reflexes. This integration occurs in the gray matter.
A reflex is a fast, predictable sequence of involuntary actions, such as muscle contractions or glandular secretions, which occurs in response to certain changes in the environment. Reflexes may be spinal or cranial and somatic or autonomic.
components of a reflex arc
- sensory receptor
- sensory neuron
- integrating center
- motor neuron
- effector
Somatic spinal reflexes include
the stretch reflex, the tendon reflex, the flexor reflex, and the crossed extensor reflex; all exhibit reciprocal innervation
A two-neuron or monosynaptic reflex arc consists of one sensory neuron and one motor neuron.
A stretch reflex, such as the patellar reflex, is an example.
A polysynaptic reflex arc contains sensory neurons, interneurons, and motor neurons
tendon reflex, flexor (withdrawal) reflex, and crossed extensor reflexes are examples.
Several important somatic reflexes are used to diagnose various disorders.
patellar reflex, Achilles reflex, Babinski sign, and abdominal reflex
major parts of the brain
- brainstem
- cerebellum
- diencephalon
- cerebrum
The brain is protected by
cranial cavity bones and the cranial meninges
The cranial meninges are continuous with the spinal meninges.
From superficial to deep, they are the dura mater, arachnoid mater, and pia mater
Blood flow to the brain
internal carotid and vertebral arteries.
Any interruption of the oxygen or glucose supply to the brain can result in weakening of, permanent damage to, or death of brain cells.
The blood–brain barrier causes different substances to move between the blood and the brain tissue at different rates and prevents the movement of some substances from blood into the brain
Cerebrospinal Fluid
- Cerebrospinal fluid is formed in the choroid plexuses and circulates through the lateral ventricles, third ventricle, fourth ventricle, subarachnoid space, and central canal. Most of the fluid is absorbed into the blood across the arachnoid granulations of the superior sagittal sinus.
- Cerebrospinal fluid provides mechanical protection, chemical protection, and circulation of nutrients
The medulla oblongata is continuous with the superior part of the spinal cord and contains both sensory tracts and motor tracts.
- It contains a cardiovascular center, which regulates heart rate and blood vessel diameter (cardiovascular center), and a medullary respiratory center, which helps control breathing.
- It also contains the gracile nucleus, cuneate nucleus, gustatory nucleus, cochlear nuclei, and vestibular nuclei, which are components of sensory pathways to the brain.
Also present in the medulla is the inferior olivary nucleus
-this provides instructions that the cerebellum uses to adjust muscle activity when you learn new motor skills. —–Other nuclei of the medulla coordinate vomiting, -swallowing, sneezing, coughing, and hiccupping.
The medulla also contains nuclei associated with these nerves
vestibulocochlear (VIII), glossopharyngeal (IX), vagus (X), accessory (XI), and hypoglossal (XII) nerves
The pons is superior to the medulla
It contains both sensory tracts and motor tracts.
Pontine nuclei relay nerve impulses related to voluntary skeletal movements from the cerebral cortex to the cerebellum.
The pons also contains the pontine respiratory group, which helps control breathing
Vestibular nuclei, which are present in the pons and medulla, are part of the equilibrium pathway to the brain.
Also present in the pons are nuclei associated with the trigeminal (V), abducens (VI), and facial (VII) nerves and the vestibular branch of the vestibulocochlear (VIII) nerve
The midbrain connects the pons and diencephalon and surrounds the aqueduct of the midbrain.
- It contains both sensory tracts and motor tracts. The superior colliculi coordinate movements of the head, eye, and trunk in response to visual stimuli;
- the inferior colliculi coordinate movements of the head, eyes, and trunk in response to auditory stimuli.
- The midbrain also contains nuclei associated with the oculomotor (III) and trochlear (IV) nerves.
A large part of the brainstem consists of small areas of gray matter and white matter called the reticular formation,
which helps maintain consciousness, causes awakening from sleep, and contributes to regulating muscle tone
The Cerebellum
- The cerebellum occupies the inferior and posterior aspects of the cranial cavity. It consists of two lateral hemispheres and a medial, constricted vermis.
- It connects to the brainstem by three pairs of cerebellar peduncles.
- The cerebellum smooths and coordinates the contractions of skeletal muscles. It also maintains posture and balance.
The diencephalon surrounds the third ventricle
it consists of the thalamus, hypothalamus, and epithalamus.
The thalamus is superior to the midbrain and contains nuclei that serve as relay stations for most sensory input to the cerebral cortex.
It also contributes to motor functions by transmitting information from the cerebellum and corpus striatum to the primary motor cortex of the cerebrum. In addition, the thalamus plays a role in maintenance of consciousness
The hypothalamus is inferior to the thalamus. It controls the autonomic nervous system, produces hormones, and regulates emotional and behavioral patterns (along with the limbic system).
The hypothalamus also contains a feeding center and satiety center, which regulate eating, and a thirst center, which regulates drinking. In addition, the hypothalamus controls body temperature by serving as the body’s thermostat. Also present in the hypothalamus is the suprachiasmatic nucleus, which regulates circadian rhythms and functions as the body’s internal biological clock
The epithalamus consists of the pineal gland and the habenular nuclei.
The pineal gland secretes melatonin, which is thought to promote sleep and to help set the body’s biological clock
The cerebrum is the largest part of the brain.
Its cortex contains cerebral gyri, cerebral and interlobar sulci, and cerebral fissures
The cerebrum is the largest part of the brain.
Its cortex contains cerebral gyri, cerebral and interlobar sulci, and cerebral fissures
The cerebral hemispheres are divided into four lobes:
- frontal
- parietal
- temporal
- occipita
The white matter of the cerebrum
is deep to the cortex and consists primarily of myelinated axons extending to other regions as association, commissural, and projection fibers.
The corpus striatum consists of several groups of nuclei in each cerebral hemisphere.
They help initiate and terminate movements, suppress unwanted movements, and regulate muscle tone
The limbic system encircles the upper part of the brainstem and the corpus callosum.
It functions in emotional aspects of behavior and memory
cerebral cortex
- sensory areas of the allow perception of sensory information.
- motor areas control the execution of voluntary movements.
- association areas are concerned with more complex integrative functions such as memory, personality traits, and intelligence.
primary motor cortex, which controls voluntary contractions of specific muscles or groups of muscles
premotor cortex sends impulses to the primary motor cortex that plan movements that cause specific groups of muscles to contract simultaneously and sequentially
the frontal eye field controls voluntary scanning movements of the eyes
Broca’s area, which controls production of speech
The somatosensory association area
permits you to determine the exact shape and texture of an object simply by touching it and to sense the relationship of one body part to another. It also stores memories of past somatic sensory experiences
Cranial Nerves: Overview
- Twelve pairs of cranial nerves originate from the nose, eyes, inner ear, brainstem, and spinal cord.
- They are named primarily based on their distribution and are numbered I–XII in order of attachment to the brain.
Olfactory (I) Nerve
- The olfactory (I) nerve is entirely sensory.
2. It contains axons that conduct nerve impulses for olfaction (sense of smell).
Optic (II) Nerve
- The optic (II) nerve is purely sensory.
2. It contains axons that conduct nerve impulses for vision.
Oculomotor (III), Trochlear (IV), and Abducens (VI) Nerves
- The oculomotor (III), trochlear (IV), and abducens (VI) nerves are the cranial nerves that control the muscles that move the eyeballs.
- They are all motor nerve
Trigeminal (V) Nerve
- The trigeminal (V) nerve is a mixed cranial nerve and the largest of the cranial nerves.
- It conveys touch, pain, and thermal sensations from the scalp, face, and oral cavity and controls chewing muscles and middle ear muscle.
Facial (VII) Nerve
- The facial (VII) nerve is a mixed cranial nerve.
- It conveys taste from anterior two-thirds of the tongue as well as touch, pain, and thermal sensations from skin in the external acoustic meatus; it also controls muscles of facial expression and middle ear muscle; promotes secretion of tears; and promotes secretion of saliva.
Vestibulocochlear (VIII) Nerve
- The vestibulocochlear (VIII) nerve is a sensory cranial nerve.
- It conveys sensory information for audition (hearing) and equilibrium (balance
Glossopharyngeal (IX) Nerve
- The glossopharyngeal (IX) nerve is a mixed cranial nerve.
- It conveys taste from posterior one-third of tongue, proprioception from some swallowing muscles, and touch, pain, and thermal sensations from the skin of external ear and upper pharynx; monitors blood pressure and oxygen and carbon dioxide levels in blood; assists in swallowing; and promotes secretion of saliva.
Vagus (X) Nerve
- The vagus (X) nerve is a mixed cranial nerve.
- It conveys taste from the epiglottis, proprioception from throat and voice box muscles, touch, pain, and thermal sensations from skin of external ear, and sensations from thoracic and abdominal organs; monitors blood pressure and oxygen and carbon dioxide levels in blood; promotes swallowing, vocalization, and coughing, motility and excretion of digestive canal organs, and constriction of respiratory passageways; and decreases
Accessory (XI) Nerve
- The accessory (XI) nerve is a motor cranial nerve.
2. It controls movements of the head.
Hypoglossal (XII) Nerve
- The hypoglossal (XII) nerve is a motor cranial nerve.
2. It promotes speech and swallowing
Development of the Nervous System
- The development of the nervous system begins with a thickening of a region of the ectoderm called the neural plate.
- During embryological development, primary brain vesicles form from the neural tube and serve as forerunners of various parts of the brain.
- The telencephalon forms the cerebrum, the diencephalon develops into the thalamus and hypothalamus, the mesencephalon develops into the midbrain, the metencephalon develops into the pons and cerebellum, and the myelencephalon forms the medulla.
Aging and the Nervous System
- The brain grows rapidly during the first few years of life.
- Age-related effects involve loss of brain mass and decreased capacity for sending nerve impulses.
Comparison of Somatic and Autonomic Nervous Systems
- somatic nervous system operates under conscious control
- ANS usually operates without conscious contro
Sensory input for the somatic nervous system is mainly from the somatic senses and special senses
sensory input for the ANS is from interoceptors, in addition to somatic senses and special senses.
