The Nervous System and Special Senses

1
Chapter 7

• The Nervous System and Special Senses

2

• Two communication systems of the body
• 1) nervous system
• 2) endocrine system
• The nervous system is considered the master
  controlling and communicating system of the body.
• Three overlapping functions
• 1) Monitor changes - collect stimuli or sensory
  input
• 2) Integration - process and interprets the
  sensory input and makes decisions about what
  should be done at each moment
• 3) Motor output effects a response by
  activating muscles or glands

3
(No Transcript)
4
Organization of the Nervous System

• Structural Classification
• 1) Central nervous system (CNS) consists of the
  brain and the spinal cord interpret incoming
  sensory info and issue instructions
• 2) Peripheral nervous system (PNS) consists
  mainly of the nerves that extend from the brain
  and spinal cord nerves serve as communication
  lines ( Spinal and Cranial Nerves)

5

• Functional Classification
• Concerned only w/ PNS structures
• Sensory (afferent) division consists of nerve
  fibers that convey impulses to the CNS from
  sensory receptors somatic sensory (afferent)
  fibers from skin, skeletal muscles and joints
  and visceral sensory (afferent) fibers impulses
  from visceral organs

6

• Motor (efferent) division - carries impulses
  from the CNS to effector organs, the muscles and
  glands (bring about a motor response)
• Two subdivisions of motor division
• 1) Somatic or voluntary nervous system
  consciously control skeletal muscles
• 2) Autonomic or involuntary nervous system (ANS)
  regulates events that are involuntary such as
  smooth and cardiac muscles and glands

7
Cells of Nervous System

• Supporting Cells
• Neuroglia or glia many types of cells that
  generally support, insulate, and protect the
  delicate neurons
• Types
• 1) Astrocytes star cells thread like branches
  attach to neurons and small blood vessels
• 2) Microglie small cells usually stationary
  but may perform phagocytosis
• 3) Ependymal line the cavities of the brain and
  the spinal cord beating of their cilia helps to
  circulate the cerebrospinal fluid that fills
  those cavities and forms a protective cushion
  around the CNS
• 4) Oligodendroglia hold nerve fibers together
  produce the fatty myelin sheath that surrounds
  nerve fivers located in the CNS

8
(No Transcript)
9

• Neurons
• Three parts
• 1) Cell body metabolic center
• 2) Dendrites one or more branching projections
  that transmit impulses to the neuron cell bodies
• 3) Axon the processes that transmit impulses
  away from the neuron cell bodies
• Each axonal terminal is separated from the next
  neuron by synaptic cleft.
• Axon are usually covered w/ a whitish, fatty
  material called myelin which protects, insulates
  the fibers as well as increase the transmission
  rate of nerve impulses.
• Axons outside the CNS are myelinated by Schwann
  cells. These form the myelin sheath.
• Nodes of Ranvier form at regular intervals w/
  repeated Schwann cells along the axon.

10
(No Transcript)
11

• Three types of functional neurons
• 1) Sensory(afferent) from senses to spinal cord
  and brain
• 2) Motor (efferent) away from brain and spinal
  cord to muscles and glands
• 3) Interneurons central, connecting,
  association from sensory to motor neurons

12

• Types of structural neurons
• 1) Multipolar many processes from cell body
  most common
• 2) Bipolar two processes rare in adults found
  in eye/ear where they act as sensory receptor
  cells
• 3) Unipolar single process, but is very short
  and divides almost immediately into proximal and
  distal fibers

13
(No Transcript)
14

• Nerve Impulses
• Functional Properties
• 1) Irritability ability to respond to a
  stimulus and convert it into an nerve impulse
• 2) Conductivity ability to transmit the impulse
  to other neurons, muscles or glands
• After an impulse is triggered, until
  repolarization occurs, a neuron cannot conduct
  another impulse.

15
The Nerve Impulse
16

• How neurons communicate at synapses.

17

• Reflex Arc
• Reflexes are rapid, predictable, and
  involuntary responses to stimuli occur over
  neural pathways called reflex arcs.
• Types of reflexes
• Autonomic reflexes regulate the activity of
  smooth muscles, the heart, and glands
• Somatic reflexes stimulate the skeletal muscles

18
Central Nervous System

• First appears as a simple tube, the neural tube
  during embryonic development.
• Major regions of the brain
• Cerebral hemispheres, diencephalon, brain stem,
  and cerebellum.

19

• Cerebral hemispheres most superior part of
  brain and are much larger than the other parts
  combined
• - surface exhibits elevated ridges of tissue
  called gyri, separated by shallow grooves called
  sulci. Less numerous are the deeper grooves
  called fissures.
• Lobes of the cerebral hemispheres
• Parietal lobe impulses from the bodys sensory
  receptors (except for the special senses) are
  localized and interpreted recognize pain,
  coldness, or light touch
• Occipital lobe visual senses
• Temporal lobe auditory and olfactory senses
• Frontal lobe primary motor area allows
  movement of skeletal muscles also contains
  Brocas area which is involved in the ability to
  speak and is only found in one hemisphere
  (usually left) higher intellectual reasoning are
  believed to be in the anterior part of the
  anterior part

20

• Complex memories appear to be stored in the
  temporal and frontal lobes.
• Speech area located at the junction of the
  temporal, parietal and occipital lobes
• The cell bodies of neurons involved in the
  cerebral hemisphere functions named above are
  found only in the outermost gray matter of the
  cerebrum, the cerebral cortex.

21

• The remaining cerebral hemisphere tissue the
  deeper cerebral white matter is composed of
  fiber tracts (bundles of nerve fibers) carrying
  impulses to or from the cortex.
• Corpus callosum connects the cerebral
  hemispheres

22
(No Transcript)
23

• Diencephalon (interbrain) sits atop the brain
  stem and is enclosed by cerebral hemispheres
• Thalamus relay station for sensory impulses
  passing upward to the sensory cortex start to
  recognize whether the sensation is going to be
  pleasant or unpleasant.
• Hypothalamus autonomic system plays a
  regulatory role in body temp, water balance,
  metabolism important part of the limbic system
  which is the center for many drives and emotions

24

• Pituitary gland controlled by hypothalamus
  from which it hangs produces hormones
• Mammillary bodies involved in olfaction (
  the sense of smell)
• Epithalamus parts are the pineal body (part
  of the endocrine system) the choroid plexus
  knots of capillaries w/in each ventricle, form
  the cerebrospinal fluid

25

• Brain stem diameter of your thumb and is approx
  3 inches in length provides a pathway for
  ascending and descending tracts and also has many
  gray matter areas these nuclei form the cranial
  nerves and control breathing and blood pressure.
• Parts of the brain stem
• 1) Midbrain small part of brain stem that
  extends from the mammillary bodies to the pons
  inferiorly composed of the cerebral aqueduct,
  cerebral peduncles (conveys impulses), and the
  corpora quadrigemina (involved w/ vision and
  hearing).

26

• 1) Pons means bridge mostly fiber tracts
  has important nuclei involved in the control of
  breathing
• 2) Medulla oblongata most inferior part of the
  brain stem important fiber tract area contains
  centers that control heart rate, blood pressure,
  breathing, swallowing, and vomiting
• 3) Reticular formation extends the entire
  length of the brain stem mass of gray matter
  involved in the motor control of visceral organs
  reticular activating system (RAS) plays a role
  in consciousness and the awake/sleep cycles,
  damage can result in coma

27

• Cerebellum cauliflowerlike projects dorsally
  from under the occipital lobe of the cerebrum
  has two hemispheres outer cortex of gray matter
  and an inner region of white matter provides
  precise timing for skeletal muscle activity and
  controls our balance equilibrium

28
(No Transcript)
29
Protection of the CNS

• Meninges connective tissue membranes covering
  and protecting the CNS structures
• Types
• 1) Dura mater outermost layer leathery
  double-layered membrane where it surrounds the
  brain attached to skull
• 2) Arachnoid mater middle layer weblike
  specialized projections, arachnoid villi,
  protrude through the dura mater and absorb
  cerebrospinal fluid into the venous blood in the
  dural sinuses
• 3) Pia mater delicate clings tightly to the
  surface of the brain and spinal cord, following
  every fold

30
(No Transcript)
31

• Cerebrospinal fluid(CSF) watery broth similar
  in its makeup to blood plasma in and around the
  brain and cord forming a watery cushion that
  protects from blows and other trauma
• Blood-brain barrier keeps neurons separated
  from bloodborne substances

32

• Spinal Cord
• -approx. 17 inches (42 cm)
• -provides a two-way conduction pathway to and
  from the brain
• -enclosed w/in the vertebral column
• -protected by meninges
• -31 pairs of spinal nerves arise from the cord

33
Peripheral Nervous System (PNS)

• -consists of nerves and scattered groups of
  neuronal cell bodies (ganglia)
• Structure of a Nerve
• -nerve is a bundle of neuron fibers found outside
  the CNS
• -endoneurium delicate connective tissue sheath
  that surrounds each fiber
• -perineurium coarser connective tissue wrapping
  of groups of fibers that form fascicles
• -epineurium tough fibrous sheath that bound all
  fascicles
• also have afferent and efferent nerves as CNS

34
(No Transcript)
35
Types of Nerves

• Cranial nerves primarily serve the head and
  neck only one pair (the vagus nerves) extends to
  the thoracic and abdominal cavities
• Spinal nerves 31 prs are formed by the
  combination of the ventral and dorsal roots of
  the spinal cord

36

• Remember the PNS has subdivisions autonomic
  nervous system and somatic nervous system.
• The ANS is further divided into the sympathetic
  parasympathetic divisions.
• Sympathetic fight-or-flight system activity
  when we are excited or find ourselves in
  emergency or threatening decisions
• Parasympathetic most active when the body is at
  rest and not threatened in any way