Tuesday, April 21, 2009

Beginning Ch. 48

An overview of the Nervous System

Sensory receptors collect information about the world outside the body as well as proscess information inside the body.

The Central Nervous System consists of the brain and the spinal cord. The conduction of signals from the central nervous system (CNS) to the effector cells is called motor output. Effector cells are target cells that produce some sort of response. They are generally gland or muscel cells.

The Peripheral Nervous System (PNS) consists of the nerves that commonicate motor and sensory signals in and out of the CNS. This reaches throughout the rest of the body. The PNS is divided into 2 groups

  • Somatic nervous system- directs contraction of muscles

  • Autonomic nervous system- controls organs and various involuntary muscles. broken into 2 parts

  1. Sympathetic nervous system- involved in stimulation of activities that ready the body for action (for example increasing heart rate)

  2. Parasympathetic nervous system- activates tranquil functions (stimulating secretion of saliva)

The Neuron is the functional unit of the nervous system. They are nerce cells. Neurons consist of 3 parts.

  • Cell body- contaqins the nucleus and other organelles

  • Dendrites- typically short, abundantly branched cell extensions that recieve incoming messages from other neurons

  • Axon- a single , long, slim extension of the cell body that sends nerve impulses. Covering most axons is a myelin sheath which insulates and protects it. At the end of an axon is a synaptic terminal which transmits signals to other neurons via neurotransmitters, or chemical messengers

There are 3 groups that neurons are classified in:
  1. Sensory neurons- recieve initial stimulus Ex. those in the hand stimulated by touch
  2. Motor neurons- stimulate effector cells Ex. those stimulating sweat glands to cool the body
  3. Association neurons- located in the spinal cord or brain to recieve impulses from sensory neurons or send impulses to motor neurons. (aka interneurons)

The transmitting neuron is called the presynaptic cell and the recieving neuron is called the postsynaptic cell. Ganglia are clusters of nerve cells.

Reflex arc- a rapid involuntary response to a stimulus in which a sensory nerve recieves information and passes it along to the spinal cord and then to a motor neuron, which signals an effector cell.

Glial cells are support cells. They are necessary for the proper functioning of nerve cells, and perform different functions depending on the type of glial cell.

  • Astrocytes- provide support for neurons

  • Oligodgendrocytes- form myelin sheaths around axons in the CNS

  • Schwann Cells- form myelin sheaths around axons in the PNS

1. What are the basic building blocks of the brain?

A. brain cells

B. neurons

C. neurotransmitters

D. axons

2. What is most likely to be found in a synapse?

A. cells

B. neuron

C. neurotransmitters

3. Which is/ are true?

A. a neuron doesn't go through the cell cycle

B. a nephron transmits signals throughout the body

C. the 'fight or flight' response is atributed to the sympathetic nervous system

D. A & C

1. B ; 2. C ; 3. D

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