Central Nervous System

Synapses

Incoming signals enter the neurons through _____

Dendrites

Where are synapses located?

Surface of the body

Where are 1st order neurons located?

Spinal cord

Where are 2nd order neurons located?

Brain

Where are 3rd order neurons located?

Axon to denrite

Signals in the synapse pass in a forward direction from _____

Peripheral nerves

Information enters the CNS through ______

1. Spinal cord

2. Reticular substances of medulla

3. Pons

4. Cerebellum

5. Thalamus

6. Areas of the cerebral cortex

Information enters the CNS and is conducted to multiple sensory areas:

Control bodily activities

Most important role of the motor part of the nervous system

Control of:

• Skeletal muscle contraction

• Smooth muscle contraction

• Control of secretion of chemical substances

  • by endocrine and exocrine

Bodily activities controlled by the motor part of the NS

Effectors

Muscles and glands are _____

1. Spinal cord

2. Lower brain or Subcortical

3. Higher brain or Cortical

Major levels of CNS function

Spinal cord level

Level of CNS Function

• Controls basic reflexes (e.g. knee-jerk reflex), which are automatic and don’t require conscious thought

Lower brain or Subcortical level

Level of CNS Function

• Responsible for subconscious functions (e.g. breathing, heart rate, sleep-wake cycles)

Higher brain or Cortical level

Level of CNS Function

• Responsible for higher-order functions (e.g. thought processes, memory, language, decision-making)

Action potentials

Information is transmitted in the form of _____

Chemical synapse

• Most synapses in humans are in this form

• 1st neurons secrete at its nerve ending a neurotransmitter

• Always transmit in one direction

• “transmitter substance”

Electrical synapse

• Characterized by direct fluid channels that conduct electricity from one cell to the next

• Contains small protein tubular structures called “gap junctions” - allow free movement of ions

40

There are more than _____ transmitter substances

• Acetylcholine

• Norepinephrine, epinephrine

• Histamine, glycine

• GABA, serotonin, glutamate

Most common neurotransmitters

Neuron that secretes a transmitter substance (presynaptic terminal) ; neuron on which the transmitter acts (post-synaptic terminal)

Chemical synapses always transmit it one direction, from _____ to _____

• Size of cell body

• Length, size, number of dendrites

• Length and size of axon

• Number of presynaptic terminals

Differences of neurons in the other parts of the cord and brain from the anterior motor neuron

Presynaptic terminal

• Most resemble small round or oval knobs

• “terminal knobs”, “terminal boutons”

• “synaptic knobs” or “end feet”

• Has 2 important structures:

  • mitochondria

  • transmitter vesicles

Mitochondria, Transmitter vesicles

2 important structures of the presynaptic terminal

Synaptic cleft

Separates the presynaptic terminal and post-synaptic terminal

Transmitter vesicles

Contain the transmitter substances

Mitochondria

Provide ATP needed to synthesize new transmitter substances

Depolarization

When an action potential spreads over the presynaptic terminal, what causes the transmitter vesicles to empty into the cleft?

Presynaptic membrane

Membrane of the presynaptic terminal

Voltage-gated Ca+ channels

The presynaptic membrane contains large amounts of _____

Depolarizes

When an action potential _____ the membrane, Ca+ channels allow large numbers of Ca+ ions to enter

Directly proportional

Relationship between the qty. of transmitter substance released from the terminal and the number of Ca+ ions that had entered the channel

Ca+ ions

They cause transmitter vesicles to undergo exocytosis

Receptor proteins

The membrane of the post-synaptic terminal contains large numbers of _____

• Binding component

• Ionophore component

Components of receptor proteins on the post-synaptic terminal

Binding component

• Protrudes outward from the membrane into the synaptic cleft

• Binds the neurotransmitter released from the presynaptic terminal

• Ion channel

• Second messenger activator

2 types of the Ionophore component of receptor proteins

Ion channel

Type of Ionophore

• Passes through the post-synaptic terminal membrane

Second messenger activator

Type of Ionophore

• Not an ion channel

• Molecule that protrudes and activates

• 1 or more substances in the post-synaptic terminal

• Opening of specific ion channels in the post-synaptic T

• Activation of cAMP or cGMP in the neuronal cell — metabolic activity

• Activation of one or more intracellular enzymes — chemical reaction

• Activation of gene transcription

Effects of G-protein

Alpha subunit of G-protein

Plays a key role in opening ion channels