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Mwjor division of nervous System

Central nervous system
Central Nervous System (CNS) comprises the brain and the spinal cord

Peripheral nervous system
Peripheral Nervous System (PNS) consists of everything outside the skull and spinal column


Somatic
Interacts with external environment
§ Afferent nerves
Carry sensory signals from eyes, ears, skin, etc TO CNS
§ Efferent nerves
Carry motor signals FROM CNS to skeletal muscles

afferent = toward
efferant= away


§ Autonomic
Regulates body’s internal environment
§ Afferent nerves
Carry sensory signals from internal organs TO CNS
§ Efferent nerves
Carry motor signals FROM CNS to internal organs
§ Afferent: Going towards (approach, advance)
§ Efferent: Going away (exit, escape)

1

Santiago Ramón y Cajal (1852 - 1934, a pioneer of neuroscience)
what did he do

Stained Cells
Gotgi

2

Basic structure cf cell

cell body /Soma
-rodeos

Dendrites
axon
boutons

myelin
prevent spread
improve transmission
has gaps in it!

3

3 types of neurons

muhlpolar
integrates a lot -one process emirate soma

Bipolar
-deal sensory

unipolat
pain temperature


inienneunons


Multipolar neurons have one axon and many dendrites attached
to its soma. Several dendrites allow for integration of a great deal of information.
Bipolar neurons have two processes leaving the soma. At one end, there is a single dendritic tree. They transmit sensory information (e.g. vision, audition).
Unipolar neurons have one process extending from the soma; the axon then divides into two branches. They detect touch, temperature changes, pain and other sensory events that affect the skin.
Interneurons link sensory and motor neurons.

4

The synapse ?

iunction

5

the Soma is ?

surrounded ky permeable membrane
organelles
proteins
-transporters

Cytoplam
-rlidions take places within lit

DNA in nucleus


6

protein syntho,u

DNA
MRNA

transcription = Copying dna

MRNA attaches tv ribosome

genome is protein or chromosome
-genetic Counselling

7

neurons nigh metabolic rate at neurons means need supporting cells

Neuroglia (or Glial cells)
Glia surround the neuron and support the nervous system
1. Astrocyte is a glial cell that provides physical support and cleans up debris in the brain. They control chemical composition and nourish the neuron.
2. Oligodendrocytes provide support to the axon of the cell and produce the myelin sheath which forms a tube around the axon for insulation. The sheath is not continuous; it is a series of segments. The exposed axon is called the node of Ranvier.
3. Microglia are the smallest of the glial cells. They provide an immune system for the brain and protect the brain from invading microorganisms.

Blood brain barrier

8

Blood brain barrier functions ?

Blood-brain barrier
A semipermeable barrier between the blood and the fluid that surrounds the cells of the brain
Functions of the blood-brain barrier:
1. To provide a balance between substances within neurons and in the extracellular fluid. An imbalance can disrupt the transmission of messages thus affecting brain function.
2. Impedes the passage of toxic substances.

Note on drugs that designed to get pest it

9

neuron elletnied electrical potential

action potential
-derived from squid
-Huxley cut axon = still functional!

Lrnow brow it ii measured

1. A wire electrode is placed in the extracellular fluid; it is an electrical conductor that provides a path for the electricity to enter or leave the medium.
2. A fine glass microelectrode is inserted into the axon. This records activity of the neuron.
3. The oscilloscope, a sensitive voltmeter, turns electrical fluctuations into visible signals

10

Membrane potential

The difference in the charge between the inside of the axon and the extracellular fluid is the membrane potential.
§ The neurons resting potential is when the steady membrane potential is -70mV. The inside of the axon is negative.
§ In its resting state, the neuron is polarized.
§ We can stimulate the neuron by passing a positive charge through another microelectrode. This changes the value of the membrane potential (towards zero). The neuron is now depolarized

11

action potential

The action potential is a rapid reversal of the membrane potential (i.e. the inside of the membrane becomes positive). It’s peak is +30 mV.
§ The membrane quickly restores to normal (within 2 msec), but first the potential overshoots the resting potential and becomes hyperpolarized (more negative).
§ The value of the membrane potential that must be reached to produce an action potential is called the threshold of excitation

12

threshold of excitation

The value of the membrane potential that must be reached to produce an action potential

13

ions ?

§ A ion is a charged molecule. Cations are positive, and anions are negative.
(e.g. NaCl = Na+ cation; Cl ̄ anion).
§ Forces of
diffusion move ions from high concentration to low concentrations
§ Electrostatic pressure refers to the attractive or repulsive forces between the charged ions.

§ The membrane potential is maintained by the balance of diffusion and electrostatic forces. These forces are influenced by the concentration of the fluids inside the cell (intracellular) and outside of the cell (extracellular

14

the r-sfing potential

Four important ions produce the resting potential: an organic Anion (A ̄); Sodium (Na+); potassium (K+); Chloride (Cl ̄).

The cell membrane is semipermeable: it allows certain molecules to pass but not all of them

When resting it is generally -ve and potassiun high inside cell
High Nac1 outside dell

15

the potassium sodium transporter pump ?

another force

atp

§ The sodium-potassium pump continuously pushes Na+ ions out of the cell.
§ The membrane is not very permeable to Na+ .
§ Sodium-potassium transporters, energised by adenosine triphosphate (ATP) molecules produced by the mitochondria, exchange 3 Na+ ions for

16

What causes the Action Potential?


§ The action potential occurs when there is a sudden influx of positive Na+ ions into the cell.
§ This influx is caused by a transient increase in the permeability of the membrane to NA+ which is then followed by a transient permeability to K
+.
§ This permeability is provided by ion channels that act as pores which open or close.Sibl 4 ft force

threhold at excitation must he reached
alter permeability charges polarity

see slide for diagram!

17

action potential mist move down axor called

Conduction of the Action Potential
1. The movement of the information along the axon is referred to as conduction of the action potential.
2. Conduction occurs in a unidirectional manner.
3. The size of the action potential remains constant.
4. All-or-none law states that the action potential occurs or does not occur, and once triggered, will propagate down the axon without growing or diminishing in size, to the end of the axon.
5. The rate law states that the strength of the stimulus is represented by the rate of the firing axon.
Rate cf firing is what's most imp.