Memmler’s The Human Body in Health and Disease 11th edition Chapter 9 The Nervous System: The Spinal Cord and Spinal Nerves

Role of the Nervous System Nervous system coordinates all body systems Detects and responds to stimuli Brain and spinal cord act as switching centers Nerves carry messages to and from centers

Structural Divisions Central nervous system (CNS) Brain Spinal cord Peripheral nervous system (PNS) Cranial nerves Spinal nerves

Anatomic divisions of the nervous system.

Functional Divisions Somatic nervous system Controlled voluntarily Effectors are skeletal muscles No further subdivisions Autonomic (or visceral) nervous system (ANS) Controlled involuntarily Effectors are smooth muscle, cardiac muscle, and glands Subdivided into Sympathetic nervous system Parasympathetic nervous system

Glands; Cardiac & Smooth Muscle; Brain Somatic Autonomic Skeletal; Voluntary control Glands; Cardiac & Smooth Muscle; Involuntary Sympathetic “Fight/ flight” Parasympathetic “Rest/ digest”

Checkpoint 9-1: What are the two divisions of the nervous system based on structure? Checkpoint 9-2: The nervous system can be divided functionally into two divisions based on type of control and effectors. What division is voluntary and controls skeletal muscle, and what division is involuntary and controls involuntary muscles and glands?

Neurons and Their Functions Functional cells of nervous system Highly specialized Unique structure

Diagram of a motor neuron. The break in the axon denotes length Diagram of a motor neuron. The break in the axon denotes length. The arrows show the direction of the nerve impulse. • Is the neuron shown here a sensory or a motor neuron?

Structure of a Neuron Cell body Nucleus Other organelles Cell fibers Dendrites Axons Some are protected by myelin sheath

What is a dendrite? a. A neuron fiber that conducts impulses away from the cell body b. A neuron fiber that conducts impulses to the cell body c. A gap between myelin-covered axons

Answer: b. A neuron fiber that conducts impulses to the cell body

Formation of a myelin sheath. Schwann cells wrap around the axon, creating a myelin coating. (B) The outermost layer of the Schwann cell forms the neurilemma. Spaces between the cells are the nodes (of Ranvier).

ACTIVITY Make your own myelin covered nerve

Checkpoint 9-3: The neuron, the functional unit of the nervous system, has long fibers extending from the cell body. What is the name of the fiber that carries impulses toward the cell body and what is the name of the fiber that carries impulses away from the cell body? Checkpoint 9-4: Myelin is a substance that covers and protects some axons. What color describes myelinated fibers, and what color describes unmyelinated tissue of the nervous system?

Types of Neurons Sensory neurons (afferent neurons) Conduct impulses to spinal cord, brain Motor neurons (efferent neurons) Conduct impulses to muscles, glands Interneurons (central or association neurons) Conduct information within CNS

Nerves and Tracts Nerve: fiber bundle within PNS Tract: fiber bundle within CNS Organized into fascicles Connective tissue layers Endoneurium Perineurium Epineurium

Checkpoint 9-5: Nerves are bundles of neuron fibers in the PNS Checkpoint 9-5: Nerves are bundles of neuron fibers in the PNS. These nerves may be carrying impulses either toward or away from the CNS. What name is given to nerves that convey impulses toward the CNS, and what name is given to nerves that transport away from the CNS?

Neuroglia Neuroglia (glial cells) Protect and nourish nervous tissue Support nervous tissue Aid in cell repair Remove pathogens and impurities Regulation composition of fluids around and between cells

Checkpoint 9-6: The nervous system’s nonconducting cells protect, nourish and support the neurons. What are these cells called?

The Nervous System at Work Electrical impulses sent along neuron fibers and transmitted between cells at junctions

The Nerve Impulse Plasma membrane carries electrical charge (potential) Plasma membrane is polarized (negative charge) Membrane potential reverses, generates electrical charge (action potential) Resting state Depolarization Repolarization Sodium/potassium (Na+/K+) pump Myelin sheath speeds conduction

Question: Which ions are involved in the action potential. a Question: Which ions are involved in the action potential? a. Potassium and calcium b. Sodium and oxygen c. Sodium and potassium

Answer: c. Sodium and potassium

Checkpoint 9-7: An action potential occurs in two stages Checkpoint 9-7: An action potential occurs in two stages. In the first stage, the charge on the membrane reverses, and in the second stage, it returns to the resting state. What are the names of these two stages? Checkpoint 9-8: What ions are involved in generating an action potential?

The Synapse Junction point for transmitting nerve impulse Axon (presynaptic cell) Dendrite (postsynaptic cell) Synaptic cleft Neurotransmitters Epinephrine (adrenaline) Norepinephrine (noradrenaline) Acetylcholine Receptors

Neurotransmitters and Psychoactive Drugs Psychoactive drugs affect neurotransmitter activity in the brain Used to treat depression, anxiety, obsessive-compulsive disorder (OCD) Selective serotonin reuptake inhibitors (Example: Prozac) Block serotonin uptake Others block norepinephrine, dopamine.

A synapse. The end-bulb of the presynaptic (transmitting) axon has vesicles containing neurotransmitter, which is released into the synaptic cleft to the membrane of the postsynaptic (receiving) cell. (B) Close-up of a synapse showing receptors for neurotransmitter in the postsynaptic cell membrane.

Question: The point of junction for transmitting a nerve impulse is called what? a. axon b. synapse c. vesicle

Answer: b. synapse

Checkpoint 9-9: Chemicals are needed to carry information across the synaptic cleft at a synapse. As a group, what are all these chemicals called?

The Spinal Cord Links PNS and brain Helps coordinate impulses within CNS Contained in and protected by vertebrae

Spinal cord and spinal nerves. Nerve plexuses (networks) are shown. (A) Lateral view. (B) Posterior view.  • Is the spinal cord the same length as the spinal column? How does the number of cervical vertebrae compare with the number of cervical spinal nerves?

Structure of the Spinal Cord Unmyelinated tissue (gray matter) Dorsal horn Ventral horn Gray commissure Central canal Myelinated axons (white matter) Posterior median sulcus Anterior median fissure Ascending and descending tracts

Checkpoint 9-10: The spinal cord contains both gray and white matter Checkpoint 9-10: The spinal cord contains both gray and white matter. How is this tissue arranged in the spinal cord? Checkpoint 9-11: What is the purpose of the tracts in the white matter of the spinal cord?

The spinal cord. (A) Cross-section of the spinal cord showing the organization of the gray and white matter. The roots of the spinal nerves are also shown. (B) Microscopic view of the spinal cord in cross-section (x5).

The Reflex Arc Receptor detects stimulus Sensory neuron transmits impulses to CNS CNS coordinates impulses and organizes response Motor neuron carries impulses away from CNS Effector carries out response

Typical reflex arc. Numbers show the sequence of impulses through the spinal cord (solid arrows). Contraction of the biceps brachii results in flexion of the arm at the elbow.    • Is this a somatic or an autonomic reflex arc? What type of neuron is located between the sensory and motor neuron in the CNS?

Checkpoint 9-12: What name is given to a pathway through the nervous system from a stimulus to an effector?

Reflex Activities Simple reflex Rapid Uncomplicated Automatic Spinal reflex Stretch reflex

Medical Procedures Involving the Spinal Cord Lumbar puncture (spinal tap) Cerebrospinal fluid (CSF) removed for testing Drug administration Anesthetic (an epidural or spinal anesthesia) Pain medication

Diseases and Other Disorders of the Spinal Cord Multiple sclerosis (MS) Amyotrophic lateral sclerosis Poliomyelitis Tumors Injuries Monoplegia Diplegia Paraplegia Hemiplegia Tetraplegia (Quadriplegia)

Question: In a lumbar tap, what is removed from the body for testing? a. cerebrospinal fluid b. lymph c. bone marrow

Answer: a. cerebrospinal fluid

The Spinal Nerves 31 pairs Each nerve attached to spinal cord by two roots Dorsal root Dorsal root ganglion Ventral root Nerves near end of cord travel together in the cord until each exits from its respective intervertebral foramen Mixed nerves

Branches of the Spinal Nerves Cervical plexus Phrenic nerve Brachial plexus Radial nerve Lumbosacral plexus Sciatic nerve Dermatomes

Dermatomes. A dermatome is a region of the skin supplied by a single spinal nerve. • Which spinal nerves carry impulses from the skin of the toes? From the anterior hand and fingers?

Checkpoint 9-13: How many pairs of spinal nerves are there?

Disorders of the Spinal Nerves Peripheral neuritis Sciatica Herpes zoster Guillain-Barré syndrome

The Autonomic Nervous System (ANS) Regulates the action of glands, smooth muscles of hollow organs and vessels, and heart muscle Preganglionic neuron connects spinal cord to ganglion Postganglionic neuron connects ganglion to effector

Checkpoint 9-14: How many neurons are there in each motor pathway of the ANS?

Divisions of the Autonomic Nervous System Sympathetic nervous system Parasympathetic nervous system

Sympathetic nervous system Thoracolumbar area Collateral ganglia Celiac ganglion Superior mesenteric ganglion Inferior mesenteric ganglion Adrenergic system Activated in the four E’s: excitement, emergency, embarassment, exercise

Parasympathetic nervous system Arise in craniosacral areas Terminal ganglia Cholinergic system

Question: Any group of nerve cell bodies located outside the central nervous system is known as what? a. a ganglion b. a plexus c. a horn

Answer: a. a ganglion

Autonomic nervous system Autonomic nervous system. The diagram shows only one side of the body for each division. • Which division of the autonomic nervous system has ganglia closer to the effector organ?

Cellular Receptors “Docking sites” on postsynaptic cell membranes Two types: Cholinergic receptors Nicotinic (bind nicotine) on skeletal muscle cells Muscarinic (bind muscarine, a poison) on effector cells of PNS Adrenergic receptors Found on receptor cells of sympathetic nervous system Bind norepinephrine, epinephrine

Functions of the Autonomic Nervous System Sympathetic nervous system Fight-or-flight response Parasympathetic nervous system Returns body to normal Systems generally have opposite effects on organ

Checkpoint 9-15: Which division of the ANS stimulates a stress response, and which division reverses the stress response?

Question: What is the technical name of a “docking site” on a postsynaptic cell membrane? a. neurotransmitter b. cellular receptor c. dendrite

Answer: b. cellular receptor

QUESTIONS?