Chapter 10: Nervous system Flashcards
What are the two main divisions of the nervous system?
Central nervous system and Peripheral nervous system
What does the Central nervous system consist of?
The brain and spinal cord.
What does the Peripheral nervous system consist of?
Consists of the vast network of nerves throughout the body.
Neurobiology
The study of the nervous system
What are the divisions of the Peripheral nervous system?
Sensory(afferent) and Motor(efferent)
What is the function of the Sensory(afferent) division of the Peripheral nervous system?
Carries signals from the nerve endings to CNS.
Somatic sensory of the Peripheral nervous system
Carries signals from the skin, bones, joints, and muscles
Visceral sensory of the Peripheral nervous system
Carries signals from viscera of heart, lungs, stomach, and bladder
What is the function of the Motor(efferent) division of the Peripheral nervous system?
Transmits information from CNS to rest of body
Somatic motor of the Peripheral nervous system
Allows voluntary movements of skeletal muscles
Autonomic motor of the Peripheral nervous system
Provides “automatic” activities such as control of blood pressure and heart rate.
What are the two divisions of Autonomic motor?
Sympathetic and Parasympathetic
Sympathetic division of Autonomic motor
Arouses the body for action
Parasympathetic division of Autonomic motor
Has a calming effect.
What are the two types of cells that make up the nervous system and what do they do?
Neurons: the excitable, impulse-conducting cell
Neuroglia: supportive cells, protect neurons
Types of Glial cells of CNS
Oligodendrocytes
Ependymal
Microglia
Astrocytes
Type of Glial cell of PNS
Schwann
What are the three classes of neurons?
Sensory, Interneuron, Motor
Sensory neurons
detect stimuli–such as touch, pressure, heat, cold, or chemicals and then transmit info about the stimuli to the CNS
Interneurons
(Found only in the CNS) connect the incoming sensory pathways with the outgoing motor pathways. The connections made by this neuron is what makes each of us unique in how we think, feel, and act.
Motor neurons
Relay messages from the brain to the muscle of gland cell
What are the three types of neurons?
Multipolar, Bipolar, and Unipolar
Multipolar neurons
Have one axon and multiple dendrites
Bipolar neurons
Have two processes: an axon and a dendrite with a cell body in between the two processes.
Unipolar neurons
Have one process-an axon- that extends from the cell body before branching into a T shape.
Cell body
Also called soma, is the control center of the neuron
Dendrites
Receive signals from other neurons and conduct the information to the cell body.
Axon
Carries nerve signals away from the cell body.
Myelin sheath
Consisting of mostly lipids, myelin acts to insulate the axon. (found in many but not all neurons)
Nodes of Ranvier
Gaps in the myelin sheath at evenly spaced intervals
Synaptic knob
Axon terminal ending with vesicles containing a neurotransmitter
Fast Fact: what nerve has the longest axon in the body?
The sciatic nerve extending from the base of the spine to the big toe in each foot.
How is the myelin sheath formed in the Peripheral nervous system?
Schwann cells wrap themselves around the axon, laying down multiple layers of cell membrane.
Neurilemma
Is essential for an injured nerve to regenerate.
How is the myelin sheath formed in the CNS?
Is formed by Oligodendrocytes, one oligodendrocyte forms the myelin sheath for several axons.
Does the CNS have Neurilemma?
No, which explains why CNS neurons do not regenerate.
Polarized Impulse Conduction
An excess of positive ions on one side of the membrane and an excess of negative ions on the other side.
Resting Potential
The state of being inactive and polarized; has potential to react if a stimulus comes along.
Depolarization
Stimulus causes Na+ to enter the cell
Region of interior changes from negative to positive
As the membrane becomes more positive it depolarizes
Action Potential
Channels in adjacent areas open and more Na+ enters the cell
Means the neuron has become active as it conducts an impulse along the axon
Repolarization
K+ flows out of cell
Electrical balance restored: interior has negative charge and exterior has positive charge.
However Na+ and K+ are now flip-flopped with the outside containing more K+ and the inside more Na+
Refractory Period
Membrane is polarized, but Na+ and K+ are on wrong sides of the membrane.
Sodium-potassium pump works to restore ions to rightful sides.
Impulse Conduction in Myelinated Fibers
The only place ion exchange can occur is at the nodes of Ranvier
Saltatory Conduction
Because the action potentials occur only at the nodes, the impulse seems to “leap” from node to node.
How many pair of spinal nerves are there?
31
Cervical region nerves innervate which parts of the body?
Chest, head, neck, shoulders, arms, hands, and diaphragm
Thoracic region nerves innervate which parts of the body?
Intercostal muscles of the ribcage, abdominal muscles, and back muscles.
Lumbar spinal nerves innervate which parts of the body?
Lower abdominal wall, and parts of the thighs and legs
Sacral region nerves innervate which parts of the body?
Thighs, buttocks, skin of the legs and feet, and anal and genital regions.
By adulthood which vertebra does the spinal cord extend to?
L1
Gray Matter in the spinal cord
Has a lack of myelin, contains mostly the cell bodies of motor neurons and interneurons. divided into two sets of horns (dorsal and anterior)
White Matter in the spinal cord
Abundance of myelin, contains bundles of axons called tracts that carry impulses from one part of the nervous system to another.
Epidural Space
Small space lying between the outer covering of the spinal cord and the vertebrae; contains a cushioning layer of fat.
Central canal
Minute opening that carries cerebrospinal fluid through the spinal cord.
Layers of the Meninges
Pia mater (innermost layer) Arachnoid mater (middle layer) Dura mater (tough outer layer)
Subarachnoid space
between the arachnoid mater and the pia mater, it is filled with cerebrospinal fluid.
Spinal Tracts
Bundles of axons within the white matter of the spinal cord that serve as routes of communication to and from the brain.
Ascending Tracts convey what?
Sensory signals up the spinal cord to the brain.
Descending Tracts conduct what?
Motor impulses down the spinal cord to muscles.
Dorsal Column
Ascending tract, relays sensations of deep pressure and vibration.
Spinocerebellar Tract
Ascending tract, responsible for proprioception
Spinothalamic Tract
Ascending tract, relays sensations of temperature, pressure, pain, and touch.
Corticospinal Tract or Pyramidal Tract
Descending tract, is responsible for fine movements of hands, fingers, feet and toes on the opposite side of the body.
Extrapyramidal Tracts
Descending tracts, are a group of tracts associated with balance and muscle tone.
Decussation
Most of the spinal cord tracts cross from one side of the body to the other in the brainstem.
Paraplegia
Spinal cord injury between the levels T1 and L1, paralysis in the legs
Quadriplegia
Injury above the C5 vertebrae, paralysis of all limbs
Why is an injury above the C4 so serious?
Because this is where the phrenic nerve exits the spinal cord, this nerve innervates the diaphragm so an injury here can cause respiratory failure.
Nerve
Consists of many nerve fibers encased by connective tissue
Fascicles
Nerve fibers gathered together in bundles
Mixed Nerves
Nerve that contains both sensory and motor fibers, can transmit signals in two directions
Sensory Nerves
Contain only sensory(afferent) fibers, carry sensations toward the spinal cord
Motor Nerves
Contain only motor(efferent) fibers, carry messages to muscles and glands
What are the four major plexuses of spinal nerves?
Cervical, Brachial, Lumbar, Sacral
Cervical plexus
Contains nerves that supply the muscles and skin of the neck, tops of the shoulders, and part of the head. Key nerve: Phrenic
Brachial plexus
Innervates the lower part of the shoulder and the arm. Key nerves: axillary, radial, ulnar, median
Lumbar plexus
Derived from the fibers of the first four lumbar vertebrae-supplies the thigh and leg.
Key nerve: Femoral
Sacral plexus
formed from fibers from nerves L4, L5, and S1 through S4
Key Nerve: Sciatic
Dermatomes
Specific areas of the skin that a nerve innervates
Somatic reflexes
Involve the contraction of a skeletal muscle after being stimulated by a somatic motor neuron
Cerebrum
Largest portion of the brain
Diencephalon
Sits between the cerebrum and the midbrain
Cerebellum
Second largest region of the brain
Longitudinal Fissure
A deep groove in the brain that divides the cerebrum into right and left cerebral hemispheres
Corpus Callosum
A thick bundle of nerves that run along the bottom of the fissure and serves to connect the two hemispheres
Brainstem
Makes up the rest of the brain, consists of 3 structures: Midbrain
Pons
Medulla Oblongata