A&p Ch. 11

1. Maintaining homeostasis

2. Receiving sensory input (unconscious processing of blood ph, etc)

3. Integrating information (response, stored as memory or ignored)

4. Controlling muscles & glands

5. Establishing/maintaining mental activity

1. Neurons (nerve cells) electrically excitable cells. Receive stimuli and transmit action potentials to other neurons or to effector organs. Organized to form complex networks that perform functions of nervous system.

- mostly amiotic (without mitosis)

- longest cells in the human body, both in length (up to 1 meter) and in life (over 100 years)

- high metabolic rate

- bad at anaerobic metabolism (can only live minutes without o2)

2. Glial cells (neuralgia cells) support and protect neurons. Account for over half of the brains weight. Can be more than 10-50 times more glial cells than neurons in various parts of the brain.

- protect, support and help neurons.

A ganglia is a structure containing a number of nerve cell bodies, typically linked to synapses and often form a ganglion.

A ganglion is a collection of neuron cell bodies located outside the CNS (swelling on a nerve fiber)

A plexus is an extensive network of axons and in some cases, neuron cell bodies, located outside the CNS.

Cortex (cerebral) is the thin layer of the brain that covers the outer portion. Conposed of gray matter and plays an important role in conciousness.

White matter (collection of axons) is the paler tissue of the brain and spinal cord, consisting mainly of nerve fibers with their myelin sheaths.

Areas of white matter: CNS= tracts and fibers PNS= nerves

Gray matter (collection of neuron cell bodies) is the darker tissue of the brain and spinal cord, consisting mainly of nerve cell bodies and branding dendrites.

Areas of gray matter:

CNS= cortex, nuclei, horns

PNS= ganglion

1. Neuron cell body- where nucleus lives, the source of information for protein synthesis.

Each cell body contains a single, centrally located nucleus. Extensive rough endoplasmic reticulum (ER) and the golgi apparatus surround the nucleus and mitochondria/other organelles are present.

The neurofilaments separate abundant rough ER, called nissl bodies, which are located primarily in the cell body and dendrites are the primary sites of protein synthesis in neurons.

2. Dendrites (1st cellular projection/branches/extensions) of the cell body and are the receiving portion of the neuron. They receive input from other neurons, axons, and from the environment. Many dendrite surfaces have small extensions, called dendritic spines where axons of other neurons form synapses with the dendrites. When stimulated, dendrites generate small electrical currents which are conducted toward the neuron cell body.

3. Axons (2nd cellular projection/long wire/nerve fiber) transmits action potentials to other cells. In most neurons, a single axon arises from a come shaped area of the neuron cell body called the axon hillock. As the axon hillock narrows, it transitions into the initial segment, the actual beginning of the axon. The combination of the axon hillock and the initial segment is called the trigger zone, where action potentials are generated. The cytoplasm of an axon is sometimes called the axoplasm and its plasma membrane can also be called the axolemma. Axons terminate by branching to form small extensions with enlarged ends called presynaptic terminals. These store many secretory vesicles that contain single molecules called neurotransmitters.

The functional classification for neurons is based on the direction in which action potentials are conducted.

The Afferent (sensory neurons) conduct action potentials TOWARD the CNS.

The Efferent (motor neurons) conduct action potentials AWAY from the CNS, towards muscles/glands.

Interneurons conduct action potentials within the CNS from one neuron to another.

The structural classification of neurons is based on the # of dendrites.

1. Multipolar neurons (99% of most neurons are multipolar) have many dendrites and a single axon. Located in the CNS, function as a great deal of information from other neurons.

2. Bipolar neurons (less than 1% of neurons-rare) have two processes, one dendrite and one axon. Located in some sensory organs, such as the retina of the eye & in the nasal cavity, function for the dendrite to receive the stimulus and the axon to conduct action potentials to the CNS.

3. Pseudo-unipolar neurons (mostly sensory, 1% of neurons) have a single process extending from the cell body which divides into two branches a short distance from the cell body. The two branches function as a single axon. One branch extends to the CNS and the other extends to the periphery and has dendrite like sensory receptors.

Plural form of nucleus

Action potentials occur according to the "all or none principle". If a stimulus produces a depolarizing graded potential that is large enough to reach threshold, all the permeability changes responsible for an action potential PROCEED WITHOUT STOPPING and are constant in magnitude (the all part).

If a stimulus is so weak that the depolarizing graded potential does not reach threshold, few of the permeability changes occur. The membrane potential returns to its resting level after a brief period without producing an action potential (the none part).

Threshold being the membrane potential at which voltage-gated NA+ channels open, action potentials are imitated here.