Biology 3201

Unit 1: Nervous System

What are the major parts of the Nervous System?

1. Brain2. Spinal Cord3. A series of neurons that transmit impulses

throughout the body.

The Nervous System

DRAW FIG. 12.3 PG. 393

What is the function of the Nervous System

- To help maintain homeostasis (remember- steady internal state).

- It does this by regulating body temperature, blood-glucose levels, motor coordination, among other body processes.

Structures of the Nervous System:

• There are two main sections:1. The Central Nervous System (CNS):– The Brain – The Spinal Cord

2. The Peripheral Nervous System (PNS):- The nerves that lead into and out of the central

nervous system

Function of the CNS:

• To receive sensory information, interpret that information and initiate responses such as motor responses.

Protection of the CNS:

• Four structures are used to protect the CNS. They include (i) the skull (ii) the vertebrae (iii) meninges (iv) the cerebrospinal fluid.

• The skull forms an enclosure around the brain and the vertebrae enclose the spinal cord.

• Meninges are protective membranes that surround both the brain and spinal cord.

• The cerebrospinal fluid fills the spaces within the meninges to create cushion and provide further protection.

Protection of CNS

The Spinal Cord

• The function of the spinal cord is to provide communication between the brain and the peripheral nervous system (PNS).

• The spinal cord extends from the vertebrae in the back though the bottom of the skull into the base of the brain.

• Spinal nerves will pass through the vertebrae and out to the PNS.

Spinal Cord Structure:

• A cross section of the spinal cord show the (i) central canal containing cerebrospinal fluid (ii) grey matter and (iii) white matter.

• DRAW fig 12.3 p. 393.

Grey Matter and White Matter

• The grey matter is brownish-grey in color and contains sensory neurons, motor neurons and interneurons. It also contains cell bodies and non-myelinated fibres. The grey matter is found in the center of the spinal cord in the form of a letter H.

• The white matter is found around the grey matter. It contains the myelinated axons of interneurons that run together in tracts. Ascending tracts carry information to the brain whereas descending tracts carry information from the brain.

The Brain- 4 Lobes

The Brain- 2 Hemispheres

Structure and Function of the Brain

• Cerebrum– Controls complex behaviour and intelligence.– Makes decisions and stores memories.– Controls voluntary muscles (ones you can

consciously move).– Collects info from our senses and sorts it.– Makes us different from other mammals (we have

more cerebrum tissue).– Very convoluted to increase surface area.

Cerebrum

Cerebellum

• Controls motor coordination and balance.• Contains 50% of the brains neurons.• The physical skills we learn are slowly taken over by

the cerebellum and are not consciously controlled, eg. Walking, running, etc.

Medulla

• Controls involuntary life processes, heart rate, blood pressure, breathing rate.

• Swallowing, hiccuping, vomiting, coughing.

Thalamus

• Sensory relay center• Receives sensations of heat, touch, pain, cold as well

as info from muscles. • Relays mild sensations to cerebrum• Relays strong sensations for immediate action to the

hypothalamus.

Hypothalamus

• Hypothalamus • acts as the main control center for the autonomic nervous

system. • Controls the sympathetic and parasympathetic responses.• Controls hunger, temperature, aggression and other aspects

of metabolism and behavior.

Midbrain

• Short section of brainstem between the cerebrum and the pons. It is involved in sight and hearing.

Pons

• contains bundles of axons traveling between the cerebellum and rest of CNS.

• It works with the medulla to regulate breathing rate and has reflex centers involved in head movement.

Corpus Callosum

• is a series of nerve fibers that connects the left and right hemispheres of the brain.

The Nervous SystemImages with permission of Eric Chudler <chudler@u.washington.edu>

The Nervous System

• Neurons• Soma • Axon• Dendrite• Myelin sheath• Schwann cells• Synapse

• Motor neurons• Interneurons• Sensory neurons• Neurotransmitters• Action potential • Reflex arc

Nerve tissues respond to stimuli and are composed of individual cells called neurons and their associated support cells.

Nerve cells can measure up to two meters in length and are well suited to transmitting messages. These cells convert stimuli into electrochemical impulses and transmit the signals down their lengths.

Parts of the NeuronCell Body: contains a large centrally located

nucleus. Its cytoplasm contains mitochondria, lysosomes , Golgi body and rough endoplasmic reticulum

Dendrites: are the primary sites for receiving information signals from other neurons

Axon: Long cylindrical extension of the cell body. It ranges from 1mm-1m in length. It transmits waves of depolarization when receiving an impulse that is strong enough

Axon Terminal: Bud like extension of the axon. It is responsible for releasing neurotransmitters.

Myelin Sheath(Schwann cells and Nodes of Ranvier): found in the CNS and PNS in which speed is important.

It is a fatty layer that is formed by the Schwann cells that wrap around the axon.

Schwann cells line the length of the axon in the PNS. The gap between the Schwann cells is called the nodes of Ranvier. The axon is exposed in this gap and allows the impulse to jump from one node to another thereby increasing the wave of depolarization to 120m/s.

Schwann cells enable neurons to regenerate themselves in situations where damage is not severe in the PNS

Neurons and The Reflex Response

• Recall the structure of a neuron:

Know the definitions for each part of the neuron.

DRAW

Three Classes of Neurons

• 1. Sensory Neuron- take information from a sensory receptor, such as a pain receptor, to the CNS.

• 2. Interneuron- receives info from sensory neurons and other interneurons and exchanges the information among neurons in the CNS.

• 3. Motor neuron- takes info from the CNS to an effector, such as a muscle fiber or gland.

Receptors vs EffectorsReceptors Effectors

Take in stimuli (pain, smell, etc.) from the environment.

The muscles and glands of the body that carry out actions as instructed by the CNS.

Ex: Skin receptors are stimulated by pain, heat, cold, pressure, touch

Other receptors include the sensory organs: nose, eyes, ears and tongue

Ex: pulling your hand out of hot water.

What is a Reflex?

• When a certain action sets off a specific reaction automatically.

• Ex: Blinking when something moves close to your eye.

Reflex Arc• Sensory neuron, interneuron and motor neuron are

all involved in the reflex arc• During the reflex our bodies react before our brain is

aware of the stimulus• Nerve endings are the dendrites of the sensory

neuron and require a strong stimulus to activate it• The impulse travels along the sensory neuron to the

spinal cord where the signal is passed along to the interneuron

• The interneuron sends an impulse to the motor neuron

• The motor neuron causes muscles to contract and move the body away.

• Reflex action is involuntary ( but part of the somatic nervous system).

• The interneuron sends a message to the brain making the brain aware of what has happened

The Reflex ARC

DRAW P. 396

LAB #1

• Answer the pre-lab question.• Do a complete lab write-up:

Title, Problem, Hypothesis, Materials, Procedure, Observations (table), Discussion (answer questions), Conclusion.

• Pass in your lab report either in a lab notebook or a duotang folder.

DUE:

How the Neuron Works

• 1. At Rest • Not carrying an impulse.• Membrane surface is polarized (overall positive

charge on outside, negative charge on the inside).

• The difference in charge between the inside and outside is approximately -70 mV, this is the resting potential.

Diagram: on board

All-Or-None Principle

• If an axon is stimulated sufficiently (above the threshold), the axon will trigger an impulse down the length of the axon.

• The strength of the impulse will be uniform along the entire length of the axon.

• The strength of the response is independent of the strength of the stimulus.

2. Depolarization

• If the neuron is sufficiently stimulated, a wave of depolarization is triggered.

• This involves sodium channels opening and potassium channels closing. Sodium moves inside, making the inside more positively charged than the outside.

• This change in charge is called Action Potential, and starts a chain reaction of depolarization down the length of the axon. (diagram)

3. Repolarization (2 steps)

• Immediately after the Na channels have opened for depolarization, the gates of K channels re-open, Na channels close and K ions move out. This re-establishes the polarization in the area.

• To restore the “resting” ion distribution, the Na/K pump actively transports Na back outside the membrane.

• The mitochondria in the neuron uses oxygen and glucose to produce ATP, which releases the energy that fuels the Na/K pump.

• Immediately after the wave of polarization, there is a refractory period- approx. 0.001 s before the axon is ready for another impulse.

Impulse Transmission and Membrane Potential

• The membrane potential refers to the voltage that is measured before, during and after the impulse passes.

• Resting Potential is – 70 mV. The negative signs refers to the difference in charge between the inside and outside of the axon. It is more negative inside, hence, the – 70.

• Depolarization- As the sodium ions flood in, the charges switch and therefore the voltage increases to approximately +40 mV.

• Repolarization- As the potassium moves outside the axon, the voltage decreases to just below resting potential (hyperpolarized). Then rises back to resting (-70mV).

The Synapes

DRAW Fig 12.16 pg.405

Synapses

• Neurons do not touch one another; there are tiny gaps between them. These are synapses.

• Presynaptic neuron- the neuron that carries the wave of depolarization towards the gap.

• Postsynaptic neuron- the neuron that receives the stimulus.

What happens at the Synapse?

When the wave of depolarization reaches the end of the presynaptic axon, it triggers the opening of special calcium gates. The presence of calcium triggers the release of neurotransmitters from synaptic vesicles, which are located at the ends of the axon.

• The neurotransmitter diffuses into the synapse and causes either an excitatory or inhibitory response.

• Excitatory response involves the opening of sodium channels in the post-synaptic neuron triggering the wave of depolarization.

• Inhibitory response will cause the impulse to stop. It does this by opening chloride channels and causing the inside of the membrane to be more negative.

The Importance of Neurotransmitters

Neurotransmitter Effects

Acetylcholine

Noradrenaline

Glutamate

GABA

Dopamine

Serotonin

Importance of Cholinesterase

• Cholinesterase is an enzyme that works in conjunction with acetylcholine. After the acetylcholine has binded to the receptors on the postsynaptic neuron and has produced it’s desired effect, cholinesterase is released from the pre-synaptic neuron to break down the acteylcholine and bring the neuron back to rest.

STSE Drugs and Homeostasis

Diseases associated with the Nervous System

• Give a description of the disease, causes, effects and treatments of….

MeningitisMultiple SclerosisAlzheimersParkinson’sHuntington’s

Technology Used to Diagnose and Treat N.S diseases

• 1. MRI- Magnetic Resonance Imaging– Scans the brain using a combination of large

magnets, radio frequencies and computer aids to produce a detailed image of the brain or body.

– Under the influence of the magnetic field the protons of hydrogen atoms in the body line up parallel to each other. The atoms have entered a high-energy state and are unstable.

• A strong pulse of radio waves is used to knock the protons out of alignment. As the protons realign themselves, they return to a low energy state and they produce radio signals that the computer converts into a 2D or 3D image.

• See youtube video: Understanding MRIs

• 2. EEG- Electroencephalogram– Measures electrical impulse activity of the various

areas of the brain.– Pioneered by canadian Dr. Wilder Penfield.– Monitors the condition of patients during surgery.

Can be used to determine brain death.– Can diagnose disorders such as brain tumors and

epilepsy. – Used to study brain activity during sleep to help

doctors diagnose and understand sleep disorders

• 3. CAT scan- computerized Tomography– Takes cross sectional x-rays to create a 3D image

of a part of the body. Can be rotated and viewed “slice by slice” to look for abnormalities.

The EYE

• Complete the worksheets on the eye’s structures and their functions.

The Eye

The Ear

• See notes handout on the ear.

Stroke and Spinal Injury

• A stroke is a sudden loss of brain function. It is caused by the interruption of flow of blood to the brain (ischemic stroke) or the rupture of blood vessels in the brain (hemorrhagic stroke).

• Treatment?– Clot-busting drugs– Surgery to remove pools of blood

Treatment of Spinal Injury

• Treatment starts with steroid drugs to reduce inflammation in the injured area and prevent further damage to cellular membranes that can cause nerve death.

• Each patient's injury is unique. Some patients require surgery to stabilise the spine, correct a gross misalignment, or to remove tissue causing cord or nerve compression. Some patients may be placed in traction and the spine allowed to heal naturally.

Importance of Glucose to N.S

• Cells within the nervous system require enormous amounts of energy to function. This energy is provided by the processing of glucose and the production of ATP within these tissues, requiring an adequate supply of carbohydrates and oxygen (Na+/K+ pump). ATP energy is required to operate the sodium-potassium pump which convert cellular chemical signals into electrical signals along a nerve cell and in between individual nerve cells (i.e., synapse).