THE NERVOUS SYSTEM

1
CHAPTER 7

• THE NERVOUS SYSTEM

2
Introduction

• The Nervous System (NS) is the master controlling
  and communicating system of the body.

3
Functions of the NS

• It uses sensory receptors to monitor changes
  occurring inside and outside the body.
• It processes and interprets the sensory input and
  makes decisions about what should be done.
• It activates muscles or glands.

4
Organization of the Nervous System

• Structural Classification Includes ALL nervous
  system organs
• Central NS (CNS) consists of the brain and
  spinal cord
• Peripheral NS (PNS) consists of the nerves that
  extend from the brain or spinal cord

5
Organization of the Nervous System

• Functional Classification
• Sensory (Afferent) Division consist of nerve
  fibers that carry impulses to the CNS from
  sensory receptors helps keep the CNS constantly
  informed of events going on both inside and
  outside the body.
• Motor (Efferent) Division carries impulses from
  the CNS to the organs, muscles, and glands to
  activate them has 2 smaller subdivisions
• Somatic NS allows us to consciously control our
  skeletal muscles (voluntary)
• Autonomic NS regulates events that are
  involuntary

6
Nervous Tissue Structure Function

• The NS is made up of 2 types of cells
  supporting cells and neurons
• Supporting Cells - Lumped together in the CNS as
  NEUROGLIA, which means nerve glue. Each
  different type of neuroglia is called GLIA. The
  CNS glia include
• Astrocytes star shaped cells that help make
  exchanges between the neurons and the
  capillaries MAKES UP NEARLY ½ OF THE NERUAL
  TISSUE
• Microglia spider shaped cells that dispose of
  debris, including bacteria and dead brain cells
• Ependymal Cells line the cavities of the brain
  and spinal cord have cilia to circulate
  cerebrospinal fluid
• Oligodendrocytes provide insulation to the
  nerve fibers

7
(No Transcript)
8
Nervous Tissue Structure Function

• Neurons Anatomy
• Also called NERVE CELLS specialized to transmit
  messages from one part of the body to another.
• All neurons have a cell body and one or more
  slender processes extending from the cell body.
• Parts of the Neuron
• Cell Body the metabolic center of the neuron
  contains organelles
• Nucleus center of the cell
• Mitochondrion gives the cell its energy
• Nissl Substance the rough ER that maintains the
  shape of the cell
• Dendrites convey incoming messages TOWARD the
  cell body
• Axons convey incoming messages AWAY from the
  cell body
• Axonal Terminals where the axons end
• Schwann Cells cells that wrap around the axon
• Nodes of Ranvier the gaps or indentions between
  the Schwann Cells

9
(No Transcript)
10
Nervous Tissue Structure Function

• Neurons Classification
• Functional Classification groups neurons
  according to the direction the nerve impulse is
  traveling 3groups
• Sensory carry impulses from sensory receptors
  to the CNS
• Motor carry impulses from the CNS to the
  muscles and glands
• Association they connect the motor and sensory
  neurons in a pathway
• Structural groups neurons according to the
  number of processes extending from the cell body
  3 groups
• Multipolar has several processes includes all
  motor and association neurons
• Bipolar has 2 processes (axon and dendrite)
  found only in the eye and ear
• Unipolar have one process includes sensory
  neurons in the PNS

11
(No Transcript)
12
Nervous Tissue Structure Function

• Physiology
• Nerve Impulse an electrochemical event,
  initiated by stimuli, that transmits to other
  neurons, muscle, or glands.
• Reflexes rapid, predictable, and involuntary
  responses to stimuli 2 types
• Autonomic Reflex secretion of saliva and
  changes in the size of the pupil
• Somatic Reflex pulling your hand away from a
  hot object

13
Reflex Arc
14
Central Nervous System

• Functional Anatomy of the Brain
• Size about 2 good fistfuls of pinkish gray
  matter
• Weight a little over 3 pounds
• 4 major parts of the brain
• Cerebrum largest part
• Cerebellum
• Brain stem
• Diencephalon

15
Parts of the Brain
16
Cerebrum

• Structure
• Consists of 2 large masses called CEREBRAL
  HEMISPHERES mirror images of each other
• 4 lobes of the cerebral hemispheres
• Frontal Lobe anterior portion of each cerebral
  hemisphere
• Parietal Lobe posterior to the frontal lobe
• Temporal Lobe lies below the frontal and
  parietal lobes
• Occipital Lobe posterior portion of each
  cerebral hemisphere
• Cerebral Cortex outermost portion of the
  cerebrum

17
Structure of the Cerebrum
18
Cerebrum

• Functions
• The cerebrum is concerned with higher brain
  functions.
• Three Functional Regions
• Motor Areas the motor area of the right
  cerebral hemisphere controls skeletal muscles on
  the left side of the body and vice versa
• Frontal Lobe PRIMARY MOTOR AREA controls
  speech, movement of the eyes, and writing
• Sensory Areas involves several lobes
• Parietal Lobe sensations from all parts of the
  skin
• Occipital Lobe vision
• Temporal Lobe hearing

19
Cerebrum

• Functions
• Three Functional Regions continued
• Association Areas function in the analysis and
  interpretation of sensory experiences and are
  involved with memory, reasoning, verbalizing,
  judgement, and emotional feelings
• Frontal Lobe concentrating, planning, problem
  solving
• Parietal Lobe understanding speech and choosing
  the words needed to express thoughts and feelings
• Temporal Lobe understanding speech and reading
  printed words, memory of visual scenes and music
• Occipital Lobe analyzing visual patterns and
  recognizing another person or an object
• Both cerebral hemispheres participate in basic
  functions. However, in most persons one side
  acts as a dominant hemisphere for certain
  functions.
• In 90 of the population, the left hemisphere is
  dominant for speech, writing, and reading.

20
Cerebellum

• The cerebellum is a large mass of tissue located
  below the occipital lobes of the cerebrum and
  posterior to the pons and medulla oblongata of
  the brainstem.
• Functions
• It communicates with other parts of the CNS
• It transmits sensory information concerning the
  position of the limbs and joints
• It stimulates skeletal muscles to cause the
  desired body movement
• It helps maintain posture
• Damage to the cerebellum can result in tremors,
  inaccurate movements of voluntary muscles, the
  loss of muscle tone, and the loss of equilibrium

21
Brainstem

• Brain Stem a bundle of nervous tissue that
  connects the cerebrum to the spinal cord
• 3 parts
• Midbrain
• A short section of the brain stem located between
  the diencephalons and pons
• Serves as a reflex center
• Responsible for moving the eyes to view something
  as the head is turned
• It contains the auditory reflex centers that
  operate when a person needs to move his/her head
  in order to hear sounds more distinctly

22
Brainstem

• 3 Parts Continued
• Pons
• Appears as a rounded bulge on the underside of
  the brain stem
• Relays impulses to and from the medulla oblongata
  to the cerebrum
• Medulla Oblongata
• An enlarged continuation of the spinal cord
  extending from the pons to the skull
• The nerve fibers that connect the brain and
  spinal cord MUST pass through the medulla olongata

23
Brain Stem
24
Diencephalon

• Located between the cerebral hemispheres and
  above the midbrain
• Contains the thalamus central relay station for
  sensory impulses ascending from other parts of
  the NS to the cerebral cortex
• Contains the hypothalamus plays a key role in
  maintaining homeostasis by regulating a variety
  of activities such as blood pressure, body
  temperature, body weight, sleep, and hunger

25
Protection of the CNS

• Nervous tissue is very soft and delicate
• Meninges - 3 connective tissue membranes
  covering and protecting the CNS structures
• Dura Mater outermost layer very tough and
  leathery
• Arachnoid Mater the middle layer weblike
• Pia Mater innermost layer clings tightly to
  the surface of the brain and spinal cord
• Cerebrospinal Fluid
• Provides a watery cushion around the brain and
  spinal cord
• Any significant change in CSF may be a sign of
  meningitis

26
Brain Dysfunctions

• Traumatic Brain Injuries
• Concussion occurs when brain injury is slight
  The victim may be dizzy, see stars, or lose
  consciousness briefly no permanent brain damage
• Contusion the result of marked tissue
  destruction can result in coma lasting from
  hours to a lifetime
• Cerebral Edema swelling of the brain due to
  inflammatory response to injury can result in
  death

27
Spinal Cord

• Structure a cylindrical shaped structure which
  is a continuation of the brain stem
• 31 pairs of spinal nerves arise from the cord and
  exit from the vertebral column to serve the body
  area close by
• Function provides a 2-way conduction pathway to
  and from the brain

28
(No Transcript)
29
Peripheral Nervous System

• Consist of nerves found outside the CNS
• Structure of a Nerve
• Nerve a bundle of neuron fibers found outside
  the CNS.
• Nerves are classified according to the direction
  in which they transmit impulses
• Mixed Nerves nerves carrying both sensory and
  motor fibers
• Sensory Nerves nerves carrying impulses toward
  the CNS
• Motor Nerves nerves carrying impulses away from
  the CNS
• Cranial Nerves - 12 pairs that arise from the
  brain and serve the head and neck
• Spinal Nerves 31 pairs that arise from the
  spinal cord and serve the limbs

30
Peripheral Nervous System

• Autonomic Nervous System
• Structure
• The motor subdivision of the PNS that controls
  body activities automatically
• Also known as the INVOLUNTARY NERVOUS SYSTEM
• Autonomic Functioning 2 divisions
• Sympathetic Division
• Referred to as the fight-or-flight system
• Its activity is evident when we are excited or
  find ourselves in emergency or threatening
  situations
• Signs of Activity pounding heart,
  deepbreathing, sweaty skin
• It allows the body to cope rapidly with
  situations that threaten homeostasis
• Parasympathetic Division
• Most active when the body is at rest and not
  threatened in any way.
• Concerned with normal digestion and elimination
  of wastes and conserving body energy
• Example Relaxing after a meal

31
Developmental Aspects of the Nervous System

• Because the NS is formed during the first month
  of embryonic development, any maternal infection
  early in pregnancy can have harmful effects on
  the fetal NS.
• One of the last areas of the CNS to mature is the
  hypothalamus, which regulates body temperature.
  This is why premature babies usually have to be
  monitored closely and put under a heating
  element.
• The brain reaches its maximum weight in the young
  adult
• Neurons die throughout life and are not replaced
  brain mass declines with age