Chapter 13.1 Pages The Nervous System

Introduction The Organization of the Nervous System

A)Introduction The Organization of the Nervous System BrainSpinal Cord Somatic Nerves Autonomic Nerves MotorSensory Nervous System Peripheral Nervous System MotorSensory Central Nervous System Sympathetic Voluntary Involuntary Sensory Motor Parasympathetic

Introduction The Organization of the Nervous System the Central Nervous System (CNS) consists of: the nerves of the brain the spinal cord acts as a coordinating centre for incoming and outgoing information

Introduction The Organization of the Nervous System the Peripheral Nervous System (PNS) consists of nerves that carry information between the organs of the body and CNS is subdivided into: the somatic nerves the autonomic nerves.

Introduction The Organization of the Nervous System the somatic nervous system controls skeletal muscle, bones, and skin sensory somatic nerves relay information about the environment to the CNS motor somatic nerves initiate a response

Introduction The Organization of the Nervous System the autonomic nervous system controls involuntary actions of the smooth muscles and heart and glands a system of two types of nerves that oppose each in action (parasympathetic versus sympathetic) Video

Anatomy of a Nerve Cell

The nervous system has two different types of cells: glial (neurological) cells and neurons.

glial cells are non- conducting cells important for the structural support and metabolism of the nerve cells. glial comes from the Greek word for “glue”

neurons are the functional units of the nervous system a cell that conduct nerve impulses all neurons contain: cell bodies dendrites axons.

Anatomy of a Nerve Cell

cell body main part of the neuron that contains the nucleus processes input from the dendrites and relays it to the axon. dendrites receive information, either from the environment or other neurons. is an extension of cytoplasm that conduct nerve impulses toward the cell body

Anatomy of a Nerve Cell axon is an extension of cytoplasm that carries the nerve impulses away from the cell body. a neuron has one axon that can form many branches. an axon carries impulses towards other neurons or to effectors. most nerves are made up of many axons held together by connective tissue.

Anatomy of a Nerve Cell

myelin sheath a white coating of fatty protein that covers the axon. produced by Schwann Cells in the PNS produced by oligodendrocytes in the CNS acts as an insulator preventing the loss of charged ions from the nerve cells – signal travels faster! an axon is said to be myelinated if it has a myelin coating

Anatomy of a Nerve Cell Medical Break ~Multiple Sclerosis (MS)~ Multiple sclerosis is a disease in which the myelin degenerates. It is currently thought that T cells, plays a key role in the development of MS. The axons themselves can also be damaged by the attacks. Symptoms of MS usually appear in episodic acute periods of worsening (relapses) or in a gradually-progressive deterioration of neurologic function, or in a combination of both

Anatomy of a Nerve Cell

nodes of Ranvier the areas between the sections of myelin sheath nerve impulses jump from one node to another which speeds up the movement of nerve impulses. nerve impulses move much faster along myelinated nerve fibres than nonmyelinated ones. speed is also affected by axon diameter, the larger the diameter the faster the axon.

Anatomy of a Nerve Cell neurilemma a thin outer membrane around the axon, found in all nerves of the peripheral nervous system formed by the Schwann cells and promotes the regeneration of the damaged axons. this is how feeling returns to areas that have been cut (only PNS!).

Anatomy of a Nerve Cell white matter (white from myelination) in the brain and grey matter (no myelin sheath) in the brain and spinal cord lack neurilemmas. this is why CNS injuries are usually permanent.

Anatomy of a Nerve Cell

Dendrites Stimulus Nucleus Cell body Axon hillock Presynaptic Cell Axon Synaptic terminals Synapse Postsynaptic Cell Neurotransmitter

Introduction to Information Processing

Introduction to Information Processing there are three stages in information processing: sensory input integration motor output

Introduction to Information Processing sensory input sensory (also called afferent) neurons transmit information from sensory receptors that detect external stimuli (light, sound, touch, heat, smell and taste) and internal stimuli the cell bodies of sensory neurons are located in clusters called ganglia which are located outside the spinal cord.

Introduction to Information Processing Integration interneurons (also called association neurons) link neurons to other neurons. interneurons are only found in the brain and spinal cord. the majority of neurons in the brain are interneurons. interneurons integrate and interpret the sensory information and connect sensory neurons to outgoing motor neurons.

Introduction to Information Processing motor output motor neurons (efferent neurons) relay information to the effectors. effectors are the cells or organs that respond to the external stimulus. Example: muscles, organs and glands.

Introduction to Information Processing Sensor Sensory input Integration Effector Motor output Peripheral nervous system (PNS) Central nervous system (CNS)

Introduction to Information Processing

Reflex Arc reflexes are involuntary and often unconscious the simplest nerve pathway is the reflex arc. a neural circuit through the spinal cord that provides a framework for a reflex action. usually does not involve the brain. Introduction to Information Processing

contains five essential components: a sensory receptor sensory neurons interneurons (found in the spinal cord usually) motor neurons the effector Introduction to Information Processing

example of a reflex arc: Patellar Reflex stimulus: tapping the tendon below the kneecap sensory receptors: detect the slight stretching of the tendon. Introduction to Information Processing

the impulse travels down the sensory neuron to the spinal cord. (from the PNS  CNS) the CNS relays a message back to PNS along two motor neurons. the impulse causes the quadriceps to contract and hamstring to relax. this causes your lower leg to rise. Introduction to Information Processing

C) Introduction to Information Processing

Try it! Questions 1-5 page 414