Nervous System Lecture Flashcards
Describe the basic definition of the nervous system.
A network of nerve cells, supporting cells, nerve fibers, and receptors that enable the body to respond to changes in the internal and external environment
Identify the subdivisions and functional components of the nervous system (e.g. CNS = brain, spinal cord, nuclei; PNS = peripheral nerves, ganglia receptors).
Central Nervous System (CNS)
- Brain
- Spinal cord
Peripheral Nervous System (PNS) - Peripheral nerves - Ganglia - Receptors
Describe the difference between ganglia and nuclei, including their locations
Nuclei –> collection of nerve cell bodies inside CNS
Ganglia –> collection of nerve cell bodies inside PNS
- Describe the basic structure of a neuron (e.g. cell body, neurolemma, nucleus, dendrites, axon, axon hillock, Nissl substance) including location and function.
Neurons –> Character cells of the nervous system. Form synapses with other neurons.
Components
- Cell body containing nucleus and cytoplasm (variable in size; cell membrane known as neurolemma)
- Several nerve fibers of varying length
- Cell processes (axons, dendrites)
- Rough endoplasmic reticulum (rER)
- Numerous mitochondria
- Axon hillock
- Nissl bodies (small clumps of rER seen with Toluidine Blue Stain and light microscope)
Neuroglia
= supporting cells for neurons
Astrocytes
–> largest neuroglial cells
o Function: provides nutrition and eliminates waste from neurons, covers nodes of -Ranvier, removes excess neurotransmitters from the synaptic cleft, works with pia mater in the formation of blood-brain barrier, regulates extracellular K+ concentration, forms a fine meshwork (neuropil) in areas devoid of neurons)
Oligodendrocytes
–> smaller in size than astrocytes with fewer, less branching processes, usually aligned in columns between axons,
o Function: forms myeline sheath around CNS axons
Microglia (cells of Hortega)
–> smallest neuroglial cells, small, darkly-staining, elongated nucleus with a thin layer of cytoplasm, few, highly branches cell processes
o Function: mobile, phagocytic cells. Thought to be important in removing invading organisms and neoplastic cells; removes injured cells and cell debris; moderate immune reactions
Ependymal cells
–> forms single layer of cuboidal to columnar-shaped cells lining the brain ventricles and central canal of spinal cord. Lacks an external lamina; extensive basal infoldings; luminal surface has cilia and microvilli
o Function: modified at areas within ventricles to work with capillary loops (*choroid plexus) in the transport of fluid and secreted materials to form the cerebrospinal fluid
Schwann cells
–> develop from neural crest ectoderm
o Function: support myelinated and unmyelinated neurons, removes cell debris; guides regrowth of PNS axon, insulates axons, increases speed of conduction of nerve impulses
Satellite cells
–> single layer of small cuboidal cells covering the surface of ganglia
o Function: Insulate ganglia, provide route for metabolic exchanges
Identify the composition, function, and location of the blood brain barrier and its implications in health and disease.
A network of blood vessels and tissue that is made up of closely spaced cells and helps keep harmful substances from reaching the brain
- Capillary endothelium that has tight junctions that restrict movement of water and other molecules through the intercellular space.
- External lamina covered with food processes of astrocytes
Functions:
* Selective permeability to substances
* Free passage of O2, CO2, certain lipid-soluble molecules
* Movement of K+ and dopamine restricted
Location –> absent in midline structures of the brain bordering the 3rd and 4th ventricle
Myelinated nerve fibers
axons are surrounded by concentric layers of Schwann cell or Oligodendrocyte plasma
Myelinated cells in CNS and PNS
- CNS –> found within the CNS and optic nerve
- PNS –> most peripheral cranial and spinal nerves
Schwann cells
surround a relatively short axon segment, thickness of myeline sheath controlled by Schwann cells, myelin sheaths lined up in series along axon, nodes of Ranvier
Identify the location of myelinated and unmyelinated nerves in both the CNS and PNS, including examples of each.
Myelinated
PNS –> Schwann cells
Peripheral nerve
CNS –> Oligodendrocytes
Spinal cord
Describe the mechanism of nerve impulse conduction in both myelinated and unmyelinated nerve fibers.
Unmyelinated
1. Appropriate stimulus increases cell membrane permeability at site of stimulation
2. Organization of cell membrane polarity is reversed generating an action potential
3. Wave depolarization followed by wave of repolarization moved unidirectionally over the neuron
Myelinated
1. Appropriate stimulus causes membrane depolarization of neuron, followed by repolarization
2. Depolarization moves down axon hillock to area of myelinated segment of axon
3. Electrical impulse moves over surface of myelin sheath to first node of Ranvier
4. Depolarization of axolemma occurs at first node of Ranvier
Conduction velocity
- Directly correlated to diameter of axon
- Velocity increased through myelination
A fibers
myelinated axons of large sensory nerves (touch, pressure, proprioception, heat, and cold) and all nerve fibers supplying skeletal muscle (conduction velocities up to 130 m/second)
B fibers
smaller diameter myelinated sensory fibers from skin and viscera, and preganglionic autonomic fibers (conduction velocities up to 10 m/second).
C fibers
smallest diameter fibers; unmyelinated sensory fibers carrying pain, temperature, touch and pressure from skin and viscera; postganglionic autonomic fibers (e.g. pupil diameter, heart rate, peristalsis, urination)
Synapse
electrochemical transmission sites between neurons or neurons and effector cells
- Formed at junctions with other neurons or muscle fells (neuromuscular junctions or motor end plates)
Components of synapse
- Components:
o Presynaptic membrane –> portion of the axolemma covering bulb-shaped terminal end of axon processes
o Synaptic cleft –> 6-30 nm wide gap between presynaptic and post synaptic membranes
o Post synaptic membrane –> axolemma of the neuron immediately across from the presynaptic membrane
Identify what neurotransmitters are, where they are generally located, and what they do; also give at least two examples.
Chemical substances stored within or bound to small membranous sacs (synaptic vesicles)
- Synaptic vesicles congregated within cytoplasm of terminal boutons; contain 10,000-100,000 neurotransmitter molecules
- Usually stimulate or inhibit a particular activity
o Common neurotransmitters –> acetylcholine (Ach), epinephrine/norepinephrine, serotonin, dopamine
Describe the basic definition of receptor.
A molecular structure that reacts with a single neurotransmitter
- Can be an enzyme and/or membrane structural protein
Cholinergic
- Ach used as a neurotransmitter
- Muscarinic
o Involved G-protein signaling cascade
o Predominantly involved with modulating neuron activity and decreasing cardiac activity - Nicotinic
o Subclass of cholinergic receptors
o Involves opening membrane Na+ receptors
Adrenergic
- Epinephrine and norepinephrine used as neurotransmitters
- Alpha (a)
o Stimulated vasoconstriction, dilation of pupils, relaxation or intestinal smooth muscle, contraction of internal urinary and anal sphincter smooth muscle - Beta (B)
o Cardio acceleration, increased strength of heart contractions, lipolysis. Vasodilation, relaxation of intestinal smooth muscle, relaxation of uterine smooth muscle, relaxation of urinary bladder smooth muscle
Meninges
connective tissue covering CNS
Pia mater
connective tissue layer adherent to the CNS, and dorsal and ventral roots. Vasculature layer of meninges (connects blood vessels)
Arachnoid mater
Adhered to overlying mater, except for strands of arachnoid mater that connect to the pia mater (arachnoid trabeculae). Subarachnoid space filled with CSF communicates with the 4th ventricle via pared Foramina of Luschka; enlarged in some locations to form cisterns.
Dura mater
“tough mother.” Tightly adhered to periosteum of skill; can be separated by trauma, forming an epidural space (collects blood). Separated into periosteal and meningeal layers at certain locations to form valveless channels that conduct venous space (collects blood).
Cross section morphology of spinal cord
- White matter
- Grey matter
White matter
superficial location; contains myelinated and unmyelinated axons, astrocytes, oligodendrocytes, and blood vessels.
Grey matter
located within the spinal cord in the shape of a modified “H”; consists of: neuron cell bodies and processes = majority are unmyelinated; astrocytes; oligodendrocytes; microglial cells; capillaries organized into shape
Function of spinal cord
receives sensory information from muscles, tendons, joints, ligaments, skin, and viscera. Sends motor commands to muscles and glands. Reflex center; provides subconscious responses of muscles and glands to specific stimuli, conducts information to and from the brain involved with posture, movement, and visceral aspect of behavior.
Afferent systems
(carry sensory information to the spinal cord)
o GSA = pain, temperature, touch, general proprioception
Free nerve endings – pain, temperature, touch
Pacinian corpuscles – pressure, crude touch, vibration, and tension
Meissner’s corpuscle
Efferent systems
(carry motor information from the spinal cord)
o GSE = contraction of skeletal muscle
o GVE = contraction of smooth muscle in the walls of blood vessels supplying skeletal muscle and glands of the skin
Receptor definition
A molecule inside or on the surface of a cell that binds to a specific substance and causes a specific effect in the cell.
Free nerve endings
- Numerous small terminal branches of sensory (afferent) nerve fibers
- Detection of pain, temperature, touch
- Located in supporting tissues throughout the body
- Small diameter fibers with a slow rate of conduction
Pacinian corpuscles
- Large, encapsulated receptors (1-4 mm in length); have the appearance of the “onion”
- Detect pressure, crude touch, vibration, and tension
- Located in deeper layers of the skin, ligaments, joint capsules, some serous membranes, mesenteries, some viscera, some erogenous areas
Meissner’s corpuscles
- Small, encapsulated receptors
- Located in dermal papillae of skin (*especially fingertips, soles of feet, eyelids, lips, nipples, genitalia)
Reflex
an involuntary, short term, stereotypical response serving the immediate needs of an organism
Reflex arc
any activity to a stimulus requiring an afferent-to-efferent pathway linkage
Myotatic reflex arc
simplest reflex arc; single pseudounipolar neuron; central sensory axon synapses on dendrites of alpha motor neurons in the ventral horn gray
Steps of reflex arc
- Tapping the patellar tendon stretches muscle fibers of the quadriceps femoris muscle
- Stretching of muscle fibers causes a simultaneous stretching of the outer covering of muscle spindles associated with the skeletal muscles
- Impulses are sent from the muscle spindle through the spinal nerve associated with the quadriceps muscle to the dorsal root ganglion associated with this muscle spindle
- The impulses travel in the dorsal roots and pass through the dorsal horn and intermediate gray matter
- The impulse is carried to the ventral horn gray matter where it synapses on motor neuron
- Impulses from the motor neuron exit the ventral gray matter by traveling in the ventral roots
- Impulses travel from ventral roots to join the spinal nerve which supplies motor input to the quadriceps
- The quadriceps muscle is stimulated to contract suddenly, producing rapid extension of the stifle joint
Composition of cerebrum
a convoluted cortex of gray matter covering a central mass of white matter called the medulla
Functional organization of cerebrum
Functional organization
- Frontal lobe = motor functions; higher functions (reasoning, etc)
- Parietal lobe = pain, temperature, touch, taste
- Temporal lobe = hearing
- Occipital lobe = vision
- Olfactory lobe = smell
Outer cerebral cortex of cerebrum (gray matter)
- Neurons, neuron cell processes, central nervous system
Inner medulla of cerebrum (white matter)
- Axons, central nervous system glial cells, blood vessels
Stratification of cerebrum –>
Molecular layer
Outer granular layer
Outer pyramidal cell layer
Inner granular cell layer
Inner pyramidal cell layer
Fusiform cell layer
Gross structure cerebellum
- Dorsal division of the metencephalon
- Two lateral cerebral hemispheres separated by a midline mass (vermis)
- Surface covered with narrow ridges (folia) separated by grooves (sulci)
Cerebellum function
- Receives information regarding head movements; muscle, tendon, joint, and ligaments stretch from ipsilateral (*same side of the body). Modulates pools of motor neurons in the ipsilateral spinal cord to coordinate posture and movement
Microanatomy of cerebellum
- Gray matter of cerebral cortex covers underlying white matter
o Molecular layer (outer layer)
o Purkinje cell layer (middle layer)
o Granular cell layer (inner layer) - White matter –> branches out into the cortex like branches of tree (arbor vitae)
o Cerebral peduncles (stalks of white matter connecting the cerebellum to the brain stem)
o Afferent fibers from rostral, middle, and caudal cerebellar peduncles
o Axons from Purkinje cells
Ventricle system
a number of interconnecting cavities which are remnants of the lumen of the embryonic neural tube. The chambers include two lateral ventricles connected to the third ventricle by the interventricular foramina (interventricular foramen of Monroe), and a fourth ventricle connected to a third ventricle by the mesencephalic aqueduct (aqueduct of Silvius)
Characteristics CSF
- A fluid containing of a filtrate of blood, combines with secretions of cells lining the interior of the four ventricles of the brain
- Fills the interior of the ventricle system and central canal of spinal cord
- Differs significantly from tissue fluid = less calcium, potassium, glucose, and protein; more magnesium, sodium and chloride.
Production and circulation of CSF
- Formed at specialized structures within each ventricle called choroid plexus. Choroid plexus = an extensive in-folding of ependymal/pial cells combined with a tuft of arterioles suspended between the pial layer of the developing ventricle
- Majority of CSF produced in lateral ventricles
- CSF circulation patters: lateral ventricles –> interventricular foramen –> 3rd ventricle –> mesencephalic aqueduct –> 4th ventricle –> rt. & lateral apertures –> subarachnoid space
Absorption CSF
- Rapid turnover of CSF
- Absorption of CSF occurs at arachnoid villi and is controlled by CSF/blood pressure gradients
- Arachnoid villi = evaginations of arachnoid layer into dural sinuses of the brain. Acts as pressure-dependent, unidirectional valves
Autonomic nervous system
- Not under voluntary control
- Divided into sympathetic and parasympathetic nervous systems
Preganglionic neuron
located within CNS
- Preganglionic axons
nerve fibers extending from preganglionic of PNS
- Postganglionic neuron
located in an autonomic ganglion of PNS
- Postganglionic axons
nerve fibers extending from postganglionic neuron; synapse on effector organ
Sympathetic Nervous System
- “Fight or Flight” responses
- Dilates pupils
- Relaxation of ciliary m.
- Increases HR
- Increases blood flow to skeletal muscle
- Decreased blood to skin
- Increases blood pressure
- Increases respiration
- Decreases peristalsis
- Relaxation of the muscle in bladder wall
- Sympathetic impulses from preganglionic sympathetic neurons located in the intermediolateral cell column of thoracolumbar spinal cord
- Preganglionic sympathetic axons synapse on postganglionic sympathetic neurons in sympathetic ganglia
- Postganglionic sympathetic axons synapse on structures od effector organs
Parasympathetic Nervous System
- Decreases HR
- Constricts pupil
- Constricts ciliary muscle
- Increases peristalsis
- Urination
- Defecation
- Constriction of bronchi
- Impulses originate from preganglionic parasympathetic neurons in nuclei located in the brainstem or sacral spinal cord
- Preganglionic parasympathetic axons exit midbrain and hindbrain with cranial nerves III, VII, IX & X; synapse on postganglionic parasympathetic axons of parasympathetic ganglia, usually located within the effector organ
- Postganglionic parasympathetic axons synapse on structures of effector organs
Sympathetic vs Parasympathetic
- Parasympathetic effects are more specific, discrete & local; sympathetic effects are more widespread
- Postganglionic sympathetic axons are adrenergic (release noradrenaline); post ganglionic parasympathetic axons are cholinergic (release acetylcholine); *both preganglionic parasympathetic & sympathetic axons are cholinergic (release ACH)
