• No results found

Nervous System Notes Part 1.docx

N/A
N/A
Protected

Academic year: 2020

Share "Nervous System Notes Part 1.docx"

Copied!
20
0
0

Loading.... (view fulltext now)

Full text

(1)

The Nervous System

Living cells can only survive and function within a very narrow range of

conditions. Homeostasis is the body’s ability to keep normal body functions (the internal environment) in the same stable state or order despite variation in the external environment.

Human survival depends on a system of communication between the internal environment and the external environment. Both the nervous system and the endocrine system (hormones) perform this function. Responses to

internal/external environments are made possible by the electrochemical messages relayed from the brain (nervous system) or by chemical messengers (hormones/blood).

 the main functions of the nervous system: i)

ii)

iii)

iv)

Nerves

 there are two main types of nerve cells found in the nervous system: 1) glial cells –

(2)

 a nerve is actually a bundles of individual neurons

 neurons are composed of a cell body and a number of “branch-like” extensions:

 ___________________ are short thread-like branches that surround the cell body of the neuron.

 dendrites carry received nerve impulses _____________ the cell body

 __________ are longer branches that carry impulses away from the cell body

 axons may be enclosed in a fatty coating called ________________________

 Schwann cells, a type of glial cell, form myelin by wrapping themselves around the axon.

 myelin acts as insulation for neurons by preventing the loss of charged ions. Because of this the myelin sheath increases the speed of nerve transmission.

(3)

 myelinated neurons form __________ matter in the brain and spinal cord, while the cell bodies and unmyelinated neurons form ____________ matter

 myelinated nerve fibers are covered by ________________ which, along with the Schwann cells, promotes the regeneration of the nerve fiber after trauma

 the disease multiple sclerosis (MS) causes hardened tissue to form on top of the myelin, affecting the nerve transmission. The more scar tissue there is, the worse the symptoms of MS

 depending on their structure, neurons are classified into four types:

 anaxonic neurons:

 unipolar neurons:

 bipolar neurons:

(4)

Conduction of Nerve Impulses

 neurons conduct electrochemical impulses. We call these nerve impulses (AKA ___________________). There is a chemical and electrical component: I) Electrical Event

a) Polarization (resting neuron)

- a resting nerve is said to be __________________ - ________ on the outside relative to the inside (or negative on the inside relative to the outside).

- when a neuron is resting it is at resting potential (-70 mV).

- the difference in this charge contributes to the resting potential.

- There are three contributors to the charge separation of a resting cell:

i) The biggest contributor is the _______________ Pump! - the charge difference is caused by the relative concentrations of sodium ions (Na+), potassium ions

(K+).

- Actively transports ___ sodium ions ____________ cell for every ___ potassium ions ___________; therefore there are more positively charged ions on the ________ of the cell.

ii) Large, negatively charged ____________ present

________ the cell. They are so large that they cannot pass across the membrane.

iii) The membrane is nearly impermeable to _________ ions; therefore there are more negative ions _________ the cell. - a polarized membrane has more Na+ on the __________ of the axon

than K+ on the _____________.

outside + + + + + + + + + + + + inside

(5)

-A nerve impulse is a series of _______________________! There are three components to a nerve impulse:

**Polarized (resting) state 1) Depolarization

2) Repolarization 3) Refractory Period

1) Depolarization

 The membrane is depolarized if the potential is reduced (lower than – 70 mV).

 stimulation of the neuron by electrical discharge (or by application of certain chemicals) causes sodium “gates” to ___________ and therefore the axon membrane allows Na+ to

pass through.

 Na+rush into the axon (down their ____________________

________________) which causes there to be a positive charge on the inside of the axon relative to the outside

 this reverses the membrane potential from -70mV to +40mV with respect to the outside

 the membrane is said to be ____________________

outside - - - + + + + + + +  (direction of impulse) inside + + + + - - -

 once the Na1+have rushed in, the membrane becomes

impermeable to them again as the “gates” in the membrane _________________

(6)

2) Repolarization

 as the Na+ “gates” ___________, the K+ “gates” _________

 this has the effect of making the outside of the membrane more positive again, but with the Na+ and K+ on the ________

________ of the membrane

 the sodium-potassium pumps will then kick in and exchange the Na+ and K+ to restore the resting potential

3) Refractory Period

The time it takes after an action potential to reach the resting potential once again.

 Until the resting potential has been properly restored, a second action potential cannot be conducted along the axon.

 It is at least 1ms long due to the fact that for this time, the membrane cannot be made permeable to Na1+ , so these ions

cannot cause depolarization.

 The stronger the impulse, the longer it takes for the nerve to recover.

The process of polarization, depolarization and repolarization takes about 2ms!

- remember that nerves are bundles of neurons, so when one neuron “fires” an impulse it causes the neurons around it to fire as well.

- this “wave” of depolarization & repolarization, the “action

potential”/ nerve impulse, moves along the axon away from the stimulus.

(7)

II) Chemical Event

- once the impulse has traveled through the entire length of the axon, it reaches the ______________________________.

- the axon terminal is in close contact with the dendrites of another neuron or effector (gland/muscle).

- the space between the axon terminal of the presynaptic neuron and the dendrites of the postsynaptic neuron is called the _______

- the axon terminal contains numerous synaptic vesicles and mitochondria (to provide _____________). The vesicles store chemical transmitters (_____________________) - which move across the synapse to help “carry” the impulse from one neuron to another.

(8)

(9)

(http://camel2.conncoll.edu/academics/zoology/courses/zoo202/Nervous/synapse.html)

(10)

Two types of neurotransmitters

1) Excitatory

- i.e. Acetylcholine (ACh) is an excitatory neurotransmitter – it

causes the sodium channels of the post-synaptic membrane to open.

- the enzyme ______________________ (or acetylcholinesterase) is released after ACh to break it down so that the ACh doesn’t

continually try to stimulate the post-synaptic neuron.

- some of the ACh is also taken back up into the presynaptic neuron to help clear it out of the synapse.

- acetylcholine is responsible for alertness, learning and memory and is being researched in it’s possible role in Alzheimer’s disease.

- i.e. Norepinephrine is also an excitatory neurotransmitter.

2) Inhibitory

- i.e. GABA – (Gamma-aminobutyric acid)

- Triggers K+ ion channels to open, (instead of Na+), allowing them

to flow out of the post-synaptic neuron.

- Causes a ______________________ effect, bringing the neuron further from threshold potential since the outside of the neuron is even more __________ than normal!

- this makes it even more difficult to generate an action potential in the postsynaptic neuron and so it has an inhibitory effect on its activity

- problems with GABA are often found in people with epilepsy, Huntington’s disease and some people with sleep disorders

(11)

Speed of nerve impulses

- different nerves can move at different speed, depending on their function/location in the body, and their axon diameter

- myelinated neurons have a _________________ transmission speed than unmyelinated neurons (saltatory conduction: the impulse ‘jumps’ through the myelin)

- C-nerve fibers are unmyelinated and have a small diameter, and they move the slowest

- A-delta and A-beta nerve fibers are both myelinated, but A-beta nerve fibers have a larger diameter

- A-beta nerve fibers carry impulses related to touch, A-delta nerve fibers carry impulses related to initial pain, temperature and C-nerve fibers carry impulses related to pain, temperature and itch

(http://faculty.washington.edu/chudler/cv.html)

All-or-none response

- A stimulus must be large enough to start an impulse - must reach ____________________.

- Each axon’s threshold level varies.

- Increasing the stimulus strength does not increase the impulse strength – a neuron will either fire or not fire.

- This is called the __________________ response!

- the intensity of a stimulus is instead detected by increases in the _____________ of the nerve impulses.

(12)

(from Nelson Biology)

- in the diagram above, neurons A and B are excitatory neurons and neuron C is an inhibitory neuron.

- in order to stimulate neuron D, A and B must be fired at the same time, and C must not be fired at all, (C has the effect of canceling out A or B).

- some neurons require impulses from many other neurons in order to fire – this is called _________________.

Factors influencing the speed of conduction: 1)

(13)

Reflex Arc

- Simplest neural pathway since reflexes are automatic responses to sensory stimuli that occur without brain stimulation.

- Reflexes are ___________________ (autonomic NS) rather than ____________________ (somatic NS).

- they involve parts of the central nervous system (CNS) and peripheral nervous system (PNS)

- the pathway of neurons that are involved is called the reflex arc i.e. The knee jerk reflex

1. stimulus –

2. receptor –

3. sensory neuron –

4. interneuron -

5. motor neuron –

6. effector –

(14)

cross-section of spinal cord

- no neurons are connected to the brain so the brain has no role in this response

- the brain only “finds out about it” after it has occurred, through other sources (‘the kinetic response’)

- you don’t notice that your brain wasn’t involved because these type of reflexes occur at such a fast rate – the command to kick the knee is given BEFORE the blow is felt by the patient

- this type of reflex is a protective response (i.e. burning yourself)

(15)

Organization of the Nervous System

Nervous System

Central Nervous System (CNS) Peripheral Nervous System (PNS) Sensory pathways Motor pathways

Brain Spinal Cord Somatic NS Autonomic NS

Sensory Motor (voluntary)

Sympathetic Parasympathetic (involuntary)

(16)

The central nervous system (CNS) is divided into two parts: 1. The Spinal Cord

- Grey matter in center; white matter on outside.

- Connects the _______________ nervous system to the brain.

- Receives sensory information through its __________ root at the back of the cord and transfers information out through the _____________ root at the front of the cord.

- sensory nerves entering the spinal column have their cell bodies localized in a mass outside the spinal cord called a _____________

- the cell bodies of motor neurons are in the spinal cord (motor neurons are multipolar).

- the brain & spinal cord are covered by membranes called ______________. These prevent the exposure of CNS cells to bone & form the blood brain barrier.

- _______________ are spaces in the brain & spinal cord.

- a fluid called ____________________ fluid circulates within the ventricles & acts as a shock absorber & helps in nutrient transport.

- a spinal tap is a procedure that uses a needle to draw out

(17)

2. The Brain

- the brain is made up of three main sections: THE HINDBRAIN

 consists of the ________________, _____________________ and the ________.

a) cerebellum

 the cerebellum is responsible for _____________________ and ________________.

b) medulla oblongata

 the medulla oblongata lies just above the spinal cord and it controls __________, ___________, ___________,

_________________,______________ & _____________. c) pons

 the bridge between the ____________ and _____________________.

THE MIDBRAIN

 Forms part of the brain stem.

 Relays sensory information between ________ & ________ brain. THE FOREBRAIN

 consists of the _________, _____________, and __________. a) thalamus

 Sensory relay centre – it directs incoming sensory signals. b) hypothalamus

 Regulates the _____________ gland, ________________, _________________, (ANS - fight/flight response), & ______________.

 Major center for integration of the nervous & endocrine systems = ________________!!

 Controls drives such as __________, __________ & sexual desire.

(18)

c) cerebrum

 Largest part of the human brain - (80% of mass).

 The cerebral cortex surrounds the cerebrum and is composed of grey matter, the cerebral medulla is composed of white matter.

 Folded, which increases the _______________.

 Divided into two cerebral hemispheres, the left and right hemispheres.

 Right side of the brain controls the left side of the body, and the left side of the brain controls the right side of the body.

 the _____________________ is a bundle of nerve fibers that connects the hemispheres.

 the cerebral cortex can be further divided into 4 lobes: FRONTAL LOBE –

TEMPORAL LOBE –

PARIETAL LOBE –

OCCIPITAL LOBE –

(19)
(20)

 the ______________________________ (PNS) is made of somatic and autonomic nerves which extend beyond the brain and spinal cord – this allows the brain and spinal cord to communicate with the rest of the body, and vice versa

 the ______________________________ (ANS) controls the internal organs and is made up of two involuntary “systems”:

1. Sympathetic System

References

Related documents

Though private sector both provides the community with jobs and swell the budget, and creates opportu- nities for the community, particularly to attract resources in

When you take into account the expenses included in a 401k plan along with the limited investment choices that smart move usually means rolling over your 401k to an IRA. Doing

Which of the following statements best describes the SEC rules relating to bookkeeping

–  Includes elements in a DSS, plus software to provide effective support in group decision making. •  Executive support

This component of the study used a range of published data such as the Crime Survey for England and Wales, Office of National Statistics (ONS) data, police data on reported

• Sensory neurons carry impulses from the sense organs to the spinal cord and brain.. • Motor neurons carry impulses from the brain and spinal cord to muscles

conventional firms in the Basque Country and Spain, and producer co-ops (PCs) and employee owned firms elsewhere, in general we find evidence of growing group importance and

va dos de la zona media de la estancia ana li za da (nota 17). Sobre un fondo de color negro, con ser va mos elementos difí- ciles de determinar, pero realizados con un gran