Nervous System

The Cells of the Nervous System:

Neurons: Contain a relatively large cell body containing the nucleus, cytoplasm, and all the major organelles.

Dendrites, a cell process that conducts impulse toward the cell body. Axons, a cell process that conducts impulses away from the cell body.

Axons usually contain a series of enclosing cells called Schwann cells. Collectively these Schwann cells are called the myelin sheath. Axons may be branched and end up in structures called synaptic knobs. The gap between nerve cells is the synapse.

The cells bodies are located in the central nervous system.(brain and spinal cord). The cell bodies of certain nerves cluster outside of the spinal cord in aggregates called ganglia. These and the axons make up the peripheral nervous system. The major types of neurons of this system are: sensory and motor. They are connected to the central nervous system by structures called interneurons.

Supporting cells: these cells outnumber neurons 10-50 to one. They do not conduct impulses but are needed for the physical integrity of the system. Glial cells, Astrocytes and oligodendrocytes.

 

Transmission along Neurons:

 

The Resting Potential:

The cell membrane is negative just inside the cell. The cell is said to be polarized.

The membrane stores energy by holding these opposite charges apart. Positive outside and negative inside. The voltage across the membrane is called the membrane potential. This is the membrane's potential to do work. If the cell is not doing work it is called the resting potential. (-70 millivolts). When the cell is stimulated the voltage across its membrane changes and it becomes an excitable cell.

 

The plasma membrane of the neuron contain many sodium-potassium pumps. These pumps are ATP driven and collect sodium on the outside of the cell and potassium on the inside of the cell. Potassium and sodium may diffuse sparingly through the membrane, but the undisturbed cell can maintain the steep gradients with these pumps.

A change in the resting potential can affect its permeability. This is called a stimulus. If this stimulus causes a decrease from the resting potential of -70 millivolts in the direction of 0, the membrane is said to be depolarized. This creates an Action Potential.

The action potential is an all or none event. A neuron has a threshold potential -50 millivolts, this must be attained before the sodium gates open and allow the sodium to pour into the cell.

 

Nervous System (Parts and Brain)

Central Nervous System (CNS)

 

Brain:

1. Medulla Oblongata: through the autonomic nervous system, controls involuntary and visceral activities.

2. Cerebellum: controls body balance, muscular coordination and equilibrium.

3. Hypothalamus: regulates body temperature, thirst, hunger, metabolism, pleasure, pain, sex, and rage (in general it maintains the internal environment).

4. Thalamus: The center that sorts out the thousands of incoming and outgoing impulses and relays them to the various brain centers.

5. Cerebral cortex: center of all voluntary muscular control and mental activity. centers of analysis, coding, storage of information, recognition, memory, understanding, intelligence and sense integration are located here.

The brain is not a solid structure; it contains cavities called ventricles which contain a liquid called cerebrospinal fluid. The brain and spinal cord are covered by three layers of tough material called meninges

 


 

The Autonomic Nervous System:

Control of the involuntary muscles is taken care of by the autonomic nervous system. It is divided into 2 separate parts: the sympathetic and the parasympathetic systems.

Parasympathetic

Sympathetic

Heart

slows down beat

speeds up beat

Arteries

dilates; decreases pressure

constriction, increases pressure

Digestive Organs

speeds up peristalsis

slows down peristalsis

Urinary Bladder

constricts

relaxes

Bronchial Muscles

constricts

dilates

Sweat Glands

decreases secretions/maintains status quo

increases secretions/ Prepares body for action

EYE: 90% of our information comes through the sense of sight.

 


 

Parts of the eye:

 

1. Cornea: The transparent area of the sclera located at the front of the eye.

 

2. Aqueous Humor: fluid behind the cornea and in front of the lens. Helps focus light onto the retina.

 

3. Iris: Anterior choroid which regulated the amount of light entering the eye. It is pigmented and surrounds the pupil which is a hole.

 

4. Lens: A transparent protein disc that is used to focus light onto the retina. Its shape is controlled by cilliary muscles.

 

5. Vitreous Humor: fluid that fills the large central chamber of the eye. It helps focus light onto the retina.

6. Retina: The inner most layer of the eyeball. It contains photoreceptor cells that transmit signals from the optic disc to the optic nerve.

7. Rods and Cones: Rods are sensitive to light but do not distinguish colors, where as cones are responsible for daytime color vision.

8. Fovea: Area of the retina that contains the highest concentration of cones. Does not contain any rods.

9. Optic nerve: Nerve that connects the eye to the brain.

10. Blind spot: Area of the eye that does not contain any rod or cones. It is here that the eye is attached to the optic nerve.

  


 

 

Ear: Parts of the ear:

 

1. Pinna: The ear lobe which functions as a sound gatherer.

2. Outer ear (canal): A canal that connects the outer ear with the ear drum (tympanic membrane).

3. Tympanic membrane: A thin piece of tissue that blocks off the outer and middle ear. It transmits sound waves to the three tiny bones of just behind it.

4. Hammer, anvil, and stirrup( middle ear): The three bones of the middle ear. They vibrate sending the impulses to the oval window of the cochlea.

5. Semicircular canals (inner ear): Located in the inner ear and used in the sense of balance. The fluid in the canals move to notify the brain of any problems with the organisms balance.

6. Cochlea: A coiled structure located in the middle ear containing tiny hairs that change sound waves into nerve impulses.