Transcript NervousSystemPPT

Nervous System
Marieb 11.1
Classification
Anatomically
 CNS
 Brain
 PNS
 Peripheral nerves
 Spinal cord
Functionally
Somatic nervous system (SNS)
Skeletal or voluntary muscles
Autonomic nervous system (ANS)
Automatic functions
29-2
Nervous system
Computer

Input circuit

Output circuit

Simple computers (output directly
controlled by input)
Brain and spinal cord

Complex computers (input and previous
memory)
Control mechanisms in lower brain

CPU (sequence of information
processing)

Sensory receptors and nerves

Effectors and motor nerves

Spinal cord


CNS: Brain and Spinal
Cord
29-4
PNS: Cranial Nerves (12)
Marieb 13.5a
PNS: Spinal Nerves (31)

Spinal cord : Slender structure
continuous with the brain

Descends into the vertebral canal
and ends around the level of the first
or second lumbar vertebra

31 spinal segments:
 8 cervical segments
 12 thoracic segments
 5 lumbar segments
 5 sacral segments
 1 coccygeal segment
Marieb 13.6
Martini 13-11
Comparison of Somatic and Autonomic Systems
Marieb 14.2
Freeman 45-20
Meninges
Marieb 12.24a
CNS: Brain
 Four sections and three levels
 Cerebrum (higher brain):Thoughts and memory
 Diencephalons (subcortical or lower
brain):subconcious activities like arterial pressure,
emotions, feeding reflexes
 Brain stem (lower and mid brain): respiration,
visual and auditory reflexes
 Cerebellum (lower brain) :Coordination in
movement
29-11
Space Restriction and Brain Development
Marieb 12.3
CNS: Brain – Cerebrum

Largest section

Two cerebral hemispheres
 Connected by a thick bundle of nerve fibers
called the corpus callosum
 Longitudinal fissure between hemispheres


Sulci – grooves on surface
Gyri or convolutions – bumps of brain matter
29-13between sulci
Marieb 12.6ab
Previous slide
29-17
CNS: Brain – Cerebrum (cont.)
 Cortex
 Ventricles
 Outer layer – gray
matter
 Contains about 75%
of all neurons
 Interconnected
cavities within the
brain
 Filled with CSF
 Inner layer – white matter
 Functions
 Interpret sensory information
 Initiate body movements
29-18
 Stores memories and creates emotions
Ventricles of the Brain
Marieb 12.5
Diencephalon: Thalamus and Hypothalamus
Marieb 12.12
CNS: Brain – Diencephalon
 Between the cerebral hemispheres superior to the
brain stem
 Thalamus
 Relay station for sensory information going to the
cerebral cortex for interpretation
 Hypothalamus
 Maintains homeostasis by regulating vital activities
29-21
CNS: Brain – Brain Stem

Connects the cerebrum to the spinal cord

Midbrain (mesencephalon, amygdala)
 Medulla oblongata
 Just beneath
diencephalon
 Controls both visual
and auditory reflexes, eg.feeding reflexes

Pons
 Rounded bulge on
underside of brain stem
 Between midbrain and
medulla oblongata
 Regulates respiration
29-22
 Inferior portion of brain
stem
 Directly connected to
spinal cord
 Controls many vital
activities, such as heart
rate, blood pressure,
and breathing
CNS: Brain – Cerebellum

Location
 Inferior to the occipital lobes of the cerebrum
 Posterior to the pons and medulla oblongata

Coordinates
 Complex skeletal muscle contractions that are
needed for body movements
 Fine movements
29-23
Brain
CNS: Brain – Cerebrum (cont.)
 Lobes
 Frontal
 Motor areas for voluntary body
movements
Frontal
Parietal
 Parietal
 Somatosensory – interprets
sensations
 Temporal
 Auditory – interprets sounds
Temporal
Occipital
 Occipital
 Interprets what a person sees
29-24
Spinal Cord
Marieb 12.29a
Gray Matter and Spinal Roots
Marieb 12.31b
Cross-Sectional Anatomy of the Spinal Cord
 Anterior median fissure – separates anterior funiculi
 Posterior median sulcus – divides posterior funiculi
Marieb 12.31a
Gray Matter: Organization
Marieb 12.32
18_26_nerve_lymphoc.jpg
Alberts 18-26
Marieb 11.4
Neuron Structure (cont.)
 White matter – axons with
myelin sheath
Dendrites
 Schwann cells – neurological cells
 Wrap around some axons
 Cell membranes contain myelin
 Myelin insulates axons and enables
axons to send nerve impulses more
quickly
Schwann
cells
Axon
 Gray matter – axons without
myelin sheath
29-31
Marieb 11.3
Myelin Sheath and Neurilemma: Formation
Marieb 11.5abc
Freeman 45-12a
Comparison of Structural Classes of Neurons
Marieb T11.1.1
Martini 12-4
Saltatory Conduction
Marieb 11.16
Dendrites
Cell body
Nucleus
Synapse
Signal
Axon direction
Axon hillock
Presynaptic cell
Postsynaptic cell
Myelin sheath
Axon
terminals
Campbell 48.5
Structure of a Nerve
Marieb 13.3b
Nerve Impulse
 Impulse travels down axon to synaptic knob
 Vesicles or small sacs in synaptic knob

Produce chemicals called neurotransmitters
 Neurotransmitters are released by synaptic knob

Allow impulse transmission to postsynaptic
structures
 Dendrites
 Cell bodies
29-41
 Axons of other neurons
Nerve Impulse

Functions of neurotransmitters
 Cause muscles to contract or relax
 Cause glands to secrete products
 Activate or inhibit neurons
29-42
Nerve Impulse

Membrane potential
 Neuron cell membrane at rest is in a polarized state

Inside of cell membrane is negative (-90 mV)

Outside of cell membrane is positive due to more Na+ and K+
 As Na+ and K+ move into the cell, the membrane becomes
depolarized

Inside becomes more positive (+ 45 mV)

Action potential (nerve impulse) is created
 Repolarization occurs when K+ and later Na+ move to the
outside of the cell membrane
29-43

Return of the cell to polarized (resting) state
Synaptic Cleft: Information Transfer
Marieb 11.18
Type of Synapses
 Chemical , Electrical
 In electrical synapses, ionic current spreads directly from one cell to another
through tubular structures called connexons. A cluster of 100 or so connexons
forms a pathway (connection) called a GAP JUNCTION between adjacent
cells. Gap junctions are common between cardiac muscle cells (shown below,
left) and between smooth muscle cells
 Excitatory , inhibitory
 GABA, glycine- inhibitory, to lower anxiety
 Acetyl choline, serotonin, glutamine- Excitatory
 Epenepherin, Norepinepherin, dopamine are both excitatory and inhibitory
Postsynaptic
neuron
5 µm
Synaptic
terminals
of presynaptic
neurons
Campbell 48.16
Freeman 45-17a
CSF
 Cerebrospinal fluid (CSF) is a clear, colorless body fluid found in
the brain and spine. It is produced in the choroid plexuses of the ventricles of
the brain. It acts as a cushion or buffer for the brain's cortex, providing basic
mechanical and immunological protection to the brain inside the skull. The
CSF also serves a vital function in cerebral autoregulation of cerebral blood
flow.
 The CSF occupies the subarachnoid space (between the arachnoid mater and
the pia mater) and the ventricular system around and inside the brain and spinal
cord. It constitutes the content of the ventricles, cisterns, and sulci of the brain,
as well as the central canal of the spinal cord.
The CSF has two major pumps that
help to establish healthy flow. The
pump at the top of the spine is the
occiput bone which makes up the
lower portion of the skull. Flexion
and extension motions of the
occipital bone upon the atlas help
to pump CSF through the brain and
spinal cord
The other pump is at the bottom of
the spine in the sacrum. Flexion
and extension of the sacrum is also
critical to help pump the CSF
1. Lateral ventricle
2. Interventricular foramen
3. Third ventricle
4. Cerebral aqueduct
5. Fourth ventricle
6a. Median aperture 6b. Lateral aperture
6c. Central canal (spinal cord)
7. Subarachnoid space
8. Arachnoid villi
9. Dural sinuses
Marieb 12.26b
Composition
 CSF composition is similar to serum composition, besides
protein, calcium and protein concentrations which are lower
 CSF is normally as clear as water and does not contain any blood
cell (leukocytes, aka white blood cells and erythrocytes, aka red
blood cells).
 However, in infections such as meningitis, leukocytes may pass
into the CSF and after hemorrhage, red blood cells may be found
in CSF.
 Protein concentration in the CSF, usually very low, is increased in
case of infection and if CSF reabsorption at the level of the
arachnoïd villi is impaired.
 In a reverse way, glucose concentration is decreased in some
pathological conditions (tumor, acute bacterial infection, fungal
infections...)
Comparison of Average Serum and Cerebrospinal
Fluid
[7]
Substance
Cerebrospinal Fluid
Serum
Water Content (%)
99
93
Protein (mg/dL)
35
7000
Glucose (mg/dL)
60
90
Osmolarity
(mOsm/L)
295
295
Sodium (mEq/L)
138
138
Potassium (mEq/L)
2.8
4.5
Calcium (mEq/L)
2.1
4.8
Magnesium (mEq/
L)
0.3
1.7
Chloride (mEq/L)
119
102
pH
7.33
7.41
Function of CSF

Buoyancy: The actual mass of the human brain is about 1400 grams; however, the
net weight of the brain suspended in the CSF is equivalent to a mass of
25 grams.[18] The brain therefore exists in neutral buoyancy, which allows the brain to
maintain itsdensity without being impaired by its own weight, which would cut off
blood supply and kill neurons in the lower sections without CSF.[19]

Protection: CSF protects the brain tissue from injury when jolted or hit. In certain
situations such as auto accidents or sportsinjuries, the CSF cannot protect the brain from
forced contact with the skull case, causing hemorrhaging, brain damage, and sometimes
death.

Chemical stability: CSF flows throughout the inner ventricular system in the brain and
is absorbed back into the bloodstream, rinsing the metabolic waste from the central
nervous system through the blood–brain barrier. This allows for homeostatic regulation
of the distribution of neuroendocrine factors, to which slight changes can cause
problems or damage to the nervous system. For example,
high glycine concentration disrupts temperature and blood pressure control, and high
CSF pH causes dizziness andsyncope.[19]
Blood Brain Barrier
 Because the brain is so specialized many of the chemicals found in the blood
are actually toxic to the neurons in the brain. With such a specialized job one
would think that the brain itself should actually have its own separate
circulatory system.
 Unlike other parts of the body where the arteries and veins and capillaries bring
nutrients to cells and move waste out of cells, the neurons in the brain are
created with specialized capillaries made of protein fibers called “astrocytes”.
These specialized capillaries essentially filter out harmful toxins and only
allow through to the specialized brain cells healthy nutrients the brain needs.
 Alcohol too passes the Blood Brain Barrier as easily as water and that can be
very bad for brain tissue. Prescription drugs however, because they are mostly
synthetic have great difficulty in passing through this Blood Brain Barrier.
The body recognizes the synthetic material as foreign and won’t let it pass
through.
C) Myelination process
D) Unmelinated neuron