The Nervous System

1
The Nervous System

• Ch. 48-49

2
The Nervous System

• Performs three basic continuous functions
• Sensory input
• Integration
• Motor output

It Is Brain surgery
3
Sensory Input

• Sensory Receptors collect information from the
  outside environment.

4
Integration

• Input is interpreted and linked to appropriate
  responses
• Accomplished by the CNS (central nervous system)
• Brain
• Spinal cord

5
Motor Output

• Signal conduction from CNS to effector cells in
  PNS (peripheral nervous system)
• CNS is connected to effector cells via neurons,
  or nerve cells

6
(No Transcript)
7
The Nervous System
CNS

• PNS

Afferent
Efferent
Brain
Spinal Cord
Autonomic
Somatic
Sympathetic
Parasympathetic
8
Neurons and the Connections They Love

• The NEURON, or nerve cell is the functional unit
  of the nervous system.
• Composed of cell body, dendrites, axon, myelin
  sheath, synaptic terminals (bulbs)

9

• Dendrites receive afferent signals, incoming
  from other neurons or receptors
• Axon only one per neuron efferent pathway to
  other neuron or an effector cell (muscle, gland)
• Myelin sheath lipid layer that insulates axon
  produced by Schwann cells.
• Synaptic Terminals (bulbs) transmit signals from
  axon by release of neurotransmitters (Ach)
• Synaptic cleft (synapse) site of contact between
  two neurons or neuron and effector
• Postsynaptic cell the receiver.

10
Label This Drawing
A
H
B
G
F
E
D
C
11
How do Scientists Study Nerves?
12
From One Neuron to its Neighbor
13
The Simplest Nerve Circuit
The Reflex Arc Often involves only two nerve
cells, the sensory neuron and the motor neuron.
This action is not integrated by the CNS.
14
Supporting Cells

• GLIA glue
• Used to believe they were wholly supportive, new
  research says not!
• Provide nutrition and protection.
• Lead neurons from neural tube along pathway in
  embryonic development.

15
Three Types of Glial Cells

• Astrocytes form connections between capillaries
  and neurons for feeding and waste disposal in
  brain, they form tight junctions which form the
  blood-brain barrier.
• Microglial cells immune system cells which
  engulf microbes in the brain alcohol kills
  microglial cells in fetuses.
• Oligodendrocytes (CNS) and Schwann Cells (PNS)
  form around axons like burritos insulate
  electrical impulses and speed up nerve signal
  transduction.

16
How a Nerve Cell Passes a Signal

• All cells have a membrane potential, a difference
  in charge between inside and outside. Developed 2
  weeks post conception, maintained through life.
• The resting potential of an unstimulated nerve
  cell is about -70mV negative inside the cell.
• The resting membrane potential is maintained by
  the Sodium-Potassium Pump.
• Neurons have a 50X greater permeability to K
  than Na.

17
Resting MP
Extracellular 1 cation 1 anion Intracellular
1 cation 1 anion
Resting Potential Video
18
Excitable cells

• Cells in the body like muscle and nerve cells can
  create large changes in their membrane
  potentials.
• Environmental stimuli can cause these cells to
  alter their membrane potential, possibly causing
  an action potential.

19
The Action Potential in Words

• Stimulus causes Na gates to open.
• Na influx changes membrane potential.
• If Na influx is great enough to achieve
  threshold potential (-50mV), then all Na gates
  open.
• All or none phenomenonat threshold, all gates
  will be opened (below threshold, no extra gates
  will open) and stimulus is transmitted.
• Additional Na influx causes depolarization of
  membrane (action potential).
• K channels remain closed. Cell becomes positive.

20

• Repolarization begins when K gates open and Na
  gates are closed. ( 50mV)
• K ions leave the cell, causing the interior to
  become more negative.
• BUTThe ions are in reversed concentrations!
• When K gates finally close, there is slightly
  more K outside than inside hyperpolarization.
• Refractory period returns ions to resting state.
• Sodium-Potassium pump restores resting
  potentialno stimuli can be transmitted during
  this phasethe neuron is BUSY!

21
Action Potential Video
22
How Fast Are Impulses Conducted?

• Campbell p. 1020

23
How Do Muscle Contractions Fit in?

• All motor neurons are associated with muscle
  fibers at their peripheral endthe neuromuscular
  junction.
• There is a space between a neuron and a muscle
  fiberthe synaptic cleft.
• The depolarization wave cannot pass across the
  cleft!

24
Three Types of Muscle in the Body

• Cardiacfound only in the heart striated
  involuntary
• Smoothlines internal organsdigestive tract,
  blood vessels, rep. tract, bladder not striated
  involuntary.
• Skeletalattaches to skeleton striated
  voluntary multinucleate

25
General Anatomy of a Muscle
Muscle Fiber Cell w/ myofibrils
26
A Little Bit Closer
ONE MUSCLE FIBER(cell)
27
Myofibril Anatomy

• Skeletal muscle is striated
• Individual units are called sarcomeres.
• Thin filaments actin
• Thick filaments myosin

28
The Neuromuscular Junction
The Neuromuscular Junction
29
(No Transcript)
30
Signal Transduction

• The depolarization wave in the neuron cannot
  traverse the synaptic cleft.
• When action potential reaches the synaptic end
  bulb, Ca in the cleft flows into the bulbs.
• This calcium causes vesicles filled with
  neurotransmitters (acetylcholine) to migrate to
  the neural membrane.

31

• The vesicles fuse with the cell membrane and
  exocytose their contents into the synaptic cleft.
• Receptors on sarcolemma bind acetylcholine
  causing gated Na channels to open. As Na comes
  into the sarcoplasm, what happens?!
• DEPOLARIZATION !

32

• The depolarization wave (DW) passes across the
  sarcolemma which extends into the muscle fiber
  via the T-tubules.
• T-tubules have close associations with the
  sarcoplasmic reticulum (SR), the Ca warehouse.
• The DW opens gated Ca channels allowing Ca to
  flow into the sarcoplasmthis is the important
  part!!!!

33
(No Transcript)
34

• Ca binds the troponin complex.
• Once troponin is removed, the tropomyosin shifts
  away from the myosin binding sites.
• Ca serves as an enzyme cofactor with myosin and
  they become ATPase!
• The ATP is broken down into ADP and Pi. This
  allows myosin to bind to the actin filaments and
  contract the filament to the center of the
  sarcomere.

35
(No Transcript)
36
Muscle Contraction
37
(No Transcript)
38
(No Transcript)
39
So, How Do You Stop It?

• The binding of the acetylcholine receptors on the
  sarcolemma signals the release of
  acetylcholinesterase from the sarcolemma.
• This enzyme breaks down acetylcholine in the
  synaptic cleft.
• How do you get the contraction to continue?

One molecule of acetylcholinesterase breaks down
25,000 molecules of acetylcholine each second.
This speed makes possible the rapid "resetting"
of the synapse for transmission of another nerve
impulse.
40
(No Transcript)
41
Belgian Blue Bull

• The myostatin gene is effectively blocked by
  being mistranscribed (its truncated)leads to
  double-muscled animal.

42
(No Transcript)
43

• Negative Feedback Control (depends on four
  detector types so that the CNS knows what the
  muscles are doing and can make adjustments
  accordingly)
•      Muscle spindles (so-called stretch
  receptors) actually length detectors
•      Golgi tendon organs detectors of tension
  in tendons
•      Joint angle receptors indicate the angle
  of a joint
•      Skin stretch and compression receptors
  give information about how the skin is deformed
  around a joint

44
Storytime

• The Function of the Sympathetic Nervous System
  and Wartime