unit 6 Flashcards
topics
nerves
nerve impulses
division of the nervous system?
synapses
Organization of the nervous system
Central nervous system (CNS)
Brain and spinal cord
Peripheral nervous system(PNS)
all nerves
autonomic nervous system(ANS)
types of neurons function
sensory (afferent) neurons = conduct impulses to the spinal cord and brain
motor(efferent) neurons = conduct impulses away from brain and spinal cord to muscle and glands
interneurons = conduct impulse from sensory neurons to motor neurons or among a network of interneurons
also know as central or connecting neurons
cells of the nervous system
NEURONS
neuron structure: consist of 3 parts
cell body: neuron
dendrites: branching projections that conduct impulses to cell body of neuron
axon: elongated projection that conducts impulses away from cell of body neuron
cell of the nervous system
glia (neuroglia) = support cells, bringin the cell of nervous tissue together and structurally and functionally
3 types of glial cells CNS
astrocytes = star shaped cells that anchor small blood vessels to neuron
microglia = small cells that move in inflamed brain tissue carrying on phagocytosis
oligodendrocytes = form myelin sheaths on axon in the cns
schwann cells = form myelin sheaths on axons of the Pns
nerves and tracts
nerve: bundle of peripheral axons
tract = bundle of central axons
white matter = tissue composed primarily of myelinated axons (nerves or tract)
gray matter = tissue composed primarily of cell bodies and unmyelinated fibers
Nerve covering = fibrous connective tissue
endoneurium = surrounds individual fibers within a nerve
perineurium = surrounds a group (fascicle) of nerve fibers
epineurium = surrounds the entire nerve
nerve signals
the synapse = the place where impulses are transmitted from one neuron to another (postsynaptic neuron)
3 structures
synaptic knob
synaptic cleft
plasma membrane
neurotransmitter
bind to specific receptor molecule in the membrane of a postsynaptic neuron, opening ion channels and thereby stimulating impulse conduction by the membrane
reflex arcs
nerve impulses are conducted from receptors
= to effectors over neuron pathway or reflex arcs; conduction by a reflex arcs result in reflex
=The simplest reflex arcs are two-neuron arcs, consisting of sensory neurons synapsing in the spinal cord with motor neurons
=Three-neuron arcs consist of sensory neurons synapsing in the spinal cord with interneurons that synapse with motor neurons
nerve impulse
definition of a nerve impulse
=Self-propagating wave of electrical disturbance that travels along the surface of a neuron membrane (also called action potential)
=Mechanism of a nerve impulse
=At rest, the neuron’s membrane is slightly positive on the outside—polarized—from a slight excess of sodium ions (Na+) on the outside
=A stimulus triggers the opening of Na+ channels in the plasma membrane of the neuron
mechanism of a nerve impulse
=Inward movement of Na+ depolarizes the membrane by making the inside more positive than the outside at the stimulated point; this depolarization is a nerve impulse (action potential)
=The stimulated section of membrane immediately repolarizes, but by that time, the depolarization has already triggered the next section of membrane to depolarize, thus propagating a wave of electrical disturbances (depolarizations) all the way down the membrane
nerve signals
neurotransmitter = chemicals by which neurons communicate
Acetylcholine (ACh)
Catecholamines: Norepinephrine, dopamine, and serotonin
Endorphins
Enkephalins
Nitric oxide (NO)
Other compounds
components of synapse
1 = action potential conducted along axon reaches the axon
2 = action potential triggers release of neurotransmitter from vesicle
3 = neurotransmitters cross synaptic cleft and bind to postsynaptic receptors
4 = activated receptors trigger opening of ion channels, initiating a postsynaptic impulse
CNS
brain - - - - - - - - - - spinal cord
cranial nerves spinal nerves
autonomic involuntary
motor nerves
somatic(voluntary)
motor nerves
Sensory nerves
autonomic nervous system
autonomic conduction paths
sympathetic division
parasympathetic
sympathetic division structure
=Dendrites and cell bodies of sympathetic preganglionic neurons are located in the gray matter of the thoracic and upper lumbar segments of the spinal cord
=Axons leave the spinal cord in the anterior roots of spinal nerves, extend to sympathetic or collateral ganglia, and synapse with several postganglionic neurons whose axons extend to spinal or autonomic nerves to terminate in visceral effectors
=A chain of sympathetic ganglia is in front of and at each side of the spinal column
parasympathetic division
Functions
=Dominates control of many visceral effectors under normal, everyday conditions
=Counterbalances sympathetic function
=“Rest and Digest”
sympathetic division
Functions
=Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise and when strong emotions (anger, fear, hate, or anxiety) are triggered
=“Fight, Flight or Freeze”
parasympathetic division
Structure
=Parasympathetic preganglionic neurons
Have dendrites and cell bodies in the gray matter of the brainstem and the sacral segments of the spinal cord
=Terminate in parasympathetic ganglia located in the head and the thoracic and abdominal cavities close to visceral effectors
=Each parasympathetic preganglionic neuron synapses with postganglionic neurons to only one effector
autonomic conduction paths
=Consist of two-neuron relays (i.e., preganglionic neurons from the CNS to autonomic ganglia, synapses, postganglionic neurons from ganglia to visceral effectors)
=In contrast, somatic motor neurons conduct all the way from the CNS to somatic effectors with no intervening synapses
autonomic neurotransmitter
Cholinergic fibers
Preganglionic axons of parasympathetic and sympathetic systems and parasympathetic postganglionic axons release acetylcholine
Adrenergic fibers
Axons of sympathetic postganglionic neurons release norepinephrine (noradrenaline)
autonomic nervous system as a whole
Regulates the body’s automatic functions in ways that maintain or quickly restore homeostasis
===Many visceral effectors are doubly innervated (i.e., they receive fibers from parasympathetic and sympathetic divisions and are influenced in opposite ways by the two divisions)
CNS = divisions of the brain
brainstem
= medulla oblongata, pons, and midbrain
= cerebellum
= diencephalon
hypothalamus, thalamus, and pineal gland
= cerebrum
coverings and fluid spaces
midbrain
=Located at the top of the brainstem right below the cerebellum and above the pons
=All neuronal transmissions pass through the midbrain
=Helps to manage auditory and visual sensory information relays and plays a role in attention and alertness
=Motor reflexes specific to visual and auditory stimuli via cranial nerves
brainstem
Consists of three parts of brain, named in ascending order
=Medulla oblongata
=Pons
=Midbrain
Structure
=White matter with bits of gray matter scattered through it
Functions
=All three parts of brainstem conduct impulses to the higher parts of the brain
pons
=Located in the middle of the brainstem
=Relays information about motor function, eye movement, sensation, hearing and taste
=Plays a role in the autonomic nervous system
=4 cranial nerves exit from the Pons
=Involved in the reticular activating system related to sleep wake, attention and pain
Coverings and Fluid Spaces of the Brain and Spinal Cord
coverings
=Cranial bones and vertebrae
=Cerebral and spinal meninges
=Dura mater
=Pia mater
=Arachnoid mater
fluid spaces
= Subarachnoid spaces of meninges
= Central canal inside cord
= Ventricles in brain
diencephalon
Hypothalamus
= Consists mainly of the posterior pituitary gland, pituitary stalk, and gray matter
= Acts as the major center for controlling the ANS; therefore, it helps control the functioning of most internal organs
= Controls hormone secretion by anterior and posterior pituitary glands; therefore, it indirectly helps control hormone secretion by most other endocrine glands
= Contains centers for controlling body temperature, appetite, wakefulness, and pleasure
medulla oblongata
=Lies just above the foramen magnum (the opening through which the spinal cord passes)
=Assists in communication between the CNS and PNS
=4 cranial nerves exit here
=Controls autonomic nervous system functions such as
Respiration
Digestion
Heart rate
Blood vessels (BP regulation)
Swallowing
Sneezing
reticular formation
= Decides what sensory information will be sent to the cerebrum
= Acts as a “filter” for conscious awareness of sensory information
Example: You visit a small town in Italy. The first night you are there you hear the bells ringing all night from the clock tower on the church, and the frogs singing all night. You can’t sleep! Within a few days your brain has filtered these noises out and you sleep through the night.
diencephalon 2
Thalamus
=Dumbbell-shaped mass of gray matter extending toward each cerebral hemisphere
=Relays sensory impulses to cerebral cortex sensory areas
=In some way produces the emotions of pleasantness or unpleasantness associated with sensations
Pineal gland (pineal body)
=Small body resembling a pine nut behind the thalamus
=Adjusts output of “time-keeping hormone” melatonin in response to changing levels of external light (sunlight and moonlight)
cerebellum
Structure
=Second largest part of the human brain
=Gray matter outer layer is thin but highly folded, forming a large surface area for processing information
=Arbor vitae: Internal, treelike network of white matter tracts
Functions
=Helps control muscle contractions to produce coordinated movements for maintaining balance, moving smoothly, and sustaining normal postures
=Variety of additional coordinating effects, assisting the cerebrum and other regions of the brain
cerebrum
= Largest part of the human brain
= Outer layers of gray matter are the cerebral cortex; made up of lobes; composed mainly of dendrites and cell bodies of neurons
= Interior of the cerebrum composed mainly of white matter
= Tracts: Nerve fibers arranged in bundles
= Basal nuclei: Islands of gray matter regulate automatic movements and posture
= Functions of the cerebrum
= Mental processes of all types, including sensations, consciousness, memory, and voluntary control of movements
spinal cord
= Columns of white matter, composed of bundles of myelinated nerve fibers, form the outer portion of the H-shaped core of the spinal cord; bundles of axons called tracts
= Interior composed of gray matter made up mainly of neuron dendrites and cell bodies
= Spinal cord tracts provide two-way conduction paths: Ascending and descending
= Spinal cord functions as the primary center for all spinal cord reflexes; sensory tracts conduct impulses to the brain, and motor tracts conduct impulses from the brain
cranial nerves
Twelve pairs: Attached to undersurface of the brain
Connect brain with the neck and structures in the thorax and abdomen
