Chapter 2: Nervous System Flashcards
FUNCTIONS OF THE NERVOUS SYSTEM
- Coordinate movement
- Process sensory input
- Initiate & maintain life-sustaining functions
- Learn & form memories
- Experience emotions
- Control arousal
CENTRAL NERVOUS SYSTEM (CNS)
Cells of nervous system that make up brain & spinal cord
PERIPHERAL NERVOUS SYSTEM (PNS)
Nervous system cells that provide information to the brain & spinal cord
-Neural circuitry that travels outside of the spinal cord, down to the deepest layers of joints & organs
SENSORY DIVISION OF PNS
Runs from sensory organs to the CNS
- Collects information from outside (somatic sensory) & inside (visceral sensory) the body and sends impulses to the CNS
MOTOR DIVISION OF PNS
Carries nerve impulses from the CNS to muscles & glands throughout the body
- Nerve impulses stimulate muscles to contract & glands to secrete hormones
NEURONS
Nervous system cells that produce action potentials to communicate with other neurons, muscles, or glands
- Primary structural unit of the nervous system
3 TYPES OF NEURONS
- Motor Neurons
- Sensory Neurons
- Interneurons
ACTION POTENTIAL
Electrical signal produced by a neuron or muscle spindle, necessary for movement & perception
- Impulse or spike
- Rapid & substantial depolarization of the neuron’s membrane (signal must be enough to change the membrane potential on the neuron to less negative charge)
GLIA
Nervous system cell that protects & nourishes neurons
- Does NOT produce action potential
MOTOR NEURON
Transmit commands from brain & spinal cord to muscles & glands
- Dendrites receive information from other neurons, then impulse travels down the axon & out through the terminal endings that synapse onto muscle fibers
SENSORY NEURON
Transmit information into the brain & spinal cord to detect movement, sight, touch, sound & smell
- Receptors in the muscle, joints, or skin send an impulse to the cell body, which can transmit the signal to a motor neuron or interneuron
INTERNEURON
Create circuits between sensory or motor neurons & transmit information between different parts of the brain
- Can inhibit other neurons, act as “roadblock”
- Most abundant type of neuron in the nervous system
- Influenced by: Muscle Spindle & Golgi Tendon Organ (GTO)
COMPONENTS OF A NEURON
- Dendrites
- Cell Body (Soma)
- Axon
DENDRITES
Branches of the cell body that act as receivers, collecting information from other neurons
CELL BODY (SOMA)
Bulbous end of neuron that contains nucleus (DNA), the center of the cell
- Integrates information & determines if there is enough to create an action potential
AXON
Transmitter portion of neuron
- Relays signals to other neurons, muscles, or organs
MUSCLE SPINDLE
Sensory receptor within muscle that detects changes in length & helps regulate contraction
- Sends information to the sensory cell body, impulse then travels through the axon to the spinal cord
- Communicates with motor neurons or interneurons
SYNAPSE
Area between neurons or between a neuron & muscles or glands where electrical & chemical signals are transmitted
NEUROMUSCULAR JUNCTION
Synapse where the motor neuron transmits a signal to the muscle fiber, resulting in muscle contraction
- When a motor neuron that innervates a muscle is activated, acetylcholine (neurotransmitter) is released
- Binding of acetylcholine to receptors on muscle triggers cascade that results in contraction
MYELIN
Fatty sheath around the axon of a nerve that provides electrical insulation, protection, nourishment, & faster signal transmission
- Important for movement
MULTIPLE SCLEROSIS (MS)
Disease that damages myelin that surrounds an axon, causing movement disorder
CRANIAL NERVES
12 pairs of nerves that emerge from the brain or brainstem to relay pure sensory, pure motor, or sensory & motor (combination) information to the head
SOMATIC NERVOUS SYSTEM
Division of the PNS that controls voluntary movement
- Includes motor neurons that control muscle, along with sensory neurons that receive information from the muscles, skin, & joints
AUTONOMIC NERVOUS SYSTEM
Division of PNS that controls subconscious actions such as breathing, heart rate, & digestion
- Further divided into: Sympathetic Nervous System & Parasympathetic Nervous System
SYMPATHETIC NERVOUS SYSTEM
Division of Autonomic Nervous System that generates “fight or flight” response, through the release of norepinephrine
PARASYMPATHETIC NERVOUS SYSTEM
Division of Autonomic Nervous System that generates the “rest & digest” response
- Balances sympathetic response
NOREPINEPHRINE
Hormone/neurotransmitter released by the CNS & Sympathetic Nervous System
- Triggers “fight or flight” response
7 COMPONENTS OF THE CNS
- Forebrain:
- Cerebrum
- Diencephalon
- Brainstem:
- Midbrain
- Pons
- Medulla
- Cerebellum
- Spinal Cord
FOREBRAIN
Includes cerebrum & diencephalon
- Cerebrum: helps learn & control movement
- Divided into right & left cerebral
hemispheres, connected by corpus
callosum
- Diencephalon: relays & integrates information from different parts of the brain & spinal cord
BRAINSTEM
Includes midbrain, pons, & medulla
- Mediates sensory & motor control of head, neck, & face, as well as balance
- Contains sensory & motor pathways that travel to other parts of CNS
CEREBELLUM
Plans & coordinates movement
- “Little Brain”
- Contains more densely packed neurons than any other subdivision of the brain
SPINAL CORD
Transmits motor information down from the brain & sensory information up to the brain
- Contains reflex circuits
WHITE MATTER
Portion of brain & spinal cord that contains myelinated axons
- Myelin has a whitish appearance, causing this part to appear white
GRAY MATTER
Portion of brain & spinal cord that contains axons with little to no myelin & cell bodies
- Includes cell bodies & terminal endings of neurons, which have little/ no myelin
MENINGES
Three layers of membranes that protect the brain & spinal cord
- Small spaces between each meningeal layer provide nourishment through blood vessels & CSF
CEREBROSPINAL FLUID (CSF)
Clear fluid found in brain & spinal cord that protects & cleans brain
VENTRICLES
Cavities in the brain that contain CSF
CAUDA EQUINA
Bundle of spinal nerves that begins around the second lumbar vertebrae (L2), where the spinal cord ends
- Innervates the muscles of the hips, legs, pelvic organs, & sphincter
- Runs from L2 to the Sacrum
CERVICAL ENLARGEMENT
Larger diameter area of the spinal cord that contains the nerves that travel to the upper limbs
LUMBAR ENLARGEMENT
Larger diameter area of the spinal cord that contains the nerves that travel to the lower limbs
NERVE
Bundles of axons that carry information within the PNS
- Pathways connecting muscle & other organs to the spinal cord, & the spinal cord to those organs
- 3 Types: sensory (afferent), motor (efferent, & mixed
SENSORY (AFFERENT) NERVE
Bundle of axons that carries sensory information INTO the brain or spinal cord
MOTOR (EFFERENT) NERVE
Bundle of axons that carries information AWAY FROM the brain & spinal cord to muscles & glands
MIXED NERVE
Bundle of axons that carries sensory, motor, & autonomic information
SPINAL NERVES
31 pairs of nerves that emerge from the spinal cord to relay motor, sensory, & autonomic information from the neck to the feet (except for C1 spinal nerve, which transmits pure motor information)
- Control muscles in the body from neck to toes
- Divided into regions that correspond with the vertebrae from which they exit
CERVICAL NERVES
8 pairs of spinal nerves that exit the cervical region of the vertebral column above each corresponding vertebrae (except the C8 , which exits below the C7 vertebrae)
- C1-C8: control muscles of the neck, shoulders, upper limbs, & diaphragm
THORACIC NERVES
12 pairs of spinal nerves that exit the thoracic region of the vertebral column, below each corresponding vertebrae
- T1-T12: control muscles of the trunk
LUMBAR NERVES
5 pairs of spinal nerves that exit the lumbar region of the vertebral column, below each corresponding vertebrae
- L1-L5: control muscles of the pelvis & lower limbs
SACRAL NERVES
5 pairs of nerves that exit the sacral region of the vertebral column
- S1-S5: control muscles of the pelvis & lower limbs
COCCYGEAL NERVES
1 pair of spinal nerves that exits below the sacrum
- CO1: control a few muscles of the pelvis
LOWER MOTOR NEURON
PNS cell whose cell body is in the brainstem or spinal cord that innervates muscles or glands
- Carries information that leads to muscle contraction
- Can extend from any part of the brainstem or spinal cord
- Innervate each muscle, & control a collection of muscle fibers
MOTOR UNIT (MU)
Lower motor neuron & all the muscle fibers it innervates
- Small muscles can have as few as 5 muscle fibers in one MU (EX: muscles that control eye movement)
- Large muscles can have thousands of fibers in one MU (EX: Hamstrings)
- 3 MU types, corresponding to the 3 primary types of muscle fibers
SLOW (S) MOTOR UNIT
Contain slow-twitch fibers (Type I)
- Small bundle of small, Type I muscle fibers
- Can contract for many hours, even days if necessary
FAST FATIGUE-RESISTANT (FFR) MOTOR UNITS
Contain fast twitch muscle fibers (Type II)
- Moderate size bundle of moderate size, Type IIa muscle fibers
- Can contract for minutes at a time
FAST FATIGABLE (FF) MOTOR UNITS
Contain fast twitch muscle fibers (Type II)
- Large bundles of large, Type IIx muscle fibers
- Can contract for only 5-10 seconds before exhaustion
REGULATION OF MUSCULAR FORCE
Amount of force a muscle produces depends on 2 neural processes:
- Motor Unit Recruitment
- Rate Coding
MOTOR UNIT RECRUITMENT
Activation of additional, larger MU to generate greater muscular force
RATE CODING
Discharge rate of active MUs
- Frequency a motor neuron sends an action potential to its bundle of muscle fibers
- Higher rate coding= stronger contraction
ALL-OR-NONE LAW
When a motor neuron is activated, all corresponding muscle fibers contract
- MU can’t be partially activated
SIZE PRINCIPLE
Fixed, orderly recruitment of motor neurons from smallest to largest
- Low Force= S Motor Units
- Medium Force= S+FFR Motor Units
- High Force= S+FFR+FF Motor Units
MOTOR NEURON POOL
Vertical column of cell bodies within the spinal cord that innervate a single muscle
- Found in every muscle, & can span multiple segments within the spinal cord
- Can be activated by signals from the brain or from circuits within the spinal cord
UPPER MOTOR NEURON
CNS cell that synapses with lower motor neurons
- Forms pathways where information travels from the brain down to motor neuron pools
CEREBRAL CORTEX
Outermost layer of the brain, where voluntary movement begins
- Wraps around deeper layers of the brain to form folds & ridges
MOTOR CORTEX
Region of brain consisting of: Premotor Cortex, Primary Motor Cortex, & Supplementary Motor Cortex
- Voluntary movement is planned, initiated, & directed by Motor Cortex
- Communicates with lower motor neurons through neural tracts
NEURAL TRACT
Bundle of axons within the CNS that carries motor OR sensory information
- Descending= motor information to muscle
- Ascending= sensory information to brain
DESCENDING TRACT
Bundle of upper motor neuron axons that travels through the spinal cord to activate lower motor neurons
- Motor information to muscles
ASCENDING TRACT
Bundle of axons that carries sensory information through the spinal cord to the brain
- Sensory information to the brain
PROPRIOCEPTORS
Sensory receptors in the muscles & joints that transmit information to the CNS through ascending tracts
- Detect muscle tension
MUSCLE SPINDLE
Sensory receptor within the skeletal muscle belly that detects changes in muscle length, they are positioned parallel to muscle fibers which allows them to lengthen/shorten in sync with the muscle
- Detect changes in length due to Alpha-Gamma Co-activation
- Influences interneurons
GOLGI TENDON ORGAN (GTO)
Sensory receptor within the tendons of a muscle
- Detects changes in muscle tension
ALPHA-GAMMA CO-ACTIVATION
Process that allows a muscle spindle to contract at the same rate as the muscle where it resides
STRETCH REFLEX
Neural circuit that allows activation of a muscle to occur with simultaneous inhibition of its antagonist
- Muscle being stretched contracts, antagonist relaxes
STEPS OF STRETCH REFLEX
- Muscle is initially stretched
- Afferent signals are sent to the spinal cord
- Interneuron connects afferent & efferent fibers
- Efferent signals sent to the muscle to cause contraction
BASAL GANGLIA
Structures within the cerebrum that communicate with the motor cortex to help initiate movement
- Dysfunction can lead to movement disorders
PARKINSON’S DISEASE
Movement disorder caused by a deficiency of dopamine in the basal ganglia
HUNTINGTON’S DISEASE
Movement disorder caused by damage to the cells of the basal ganglia
