Biology 30 - Chapter 13

Nervous System

What does the nervous system consist of?

nerve cells

What does the nervous system use to communicate?

electrochemical signals

What does the nervous system maintain?

homeostasis

What activities of the body does the nervous system control? /4

It controls ALL the bodies activites: Reception, interpretation, sorting, transmission.

Two main divisions of the nervous system?

The central nervous system (CNS) and the peripheral nervous system (PNS).

What does the CNS consist of?

The brain and spinal cord

CNS functions? /3

Receive information, integration (organize), interpret info

What does the PNS consist of?

nerves outside the brain and spinal cord

PNS functions?

carry information to and from the CNS, transfer info from receptors, organs, muscles, and glands to the CNS

Two divisions of the PNS?

autonomic and somatic nerves

Function of autonomic nerves?

Regulates the internal environment

Is control voluntary or involuntary for autonomic nerves?

Control is involuntary

Two types of autonomic nerves?

sympathetic and parasympathetic nerves

Function of somatic nerves?

controls skeletal muscles

Is control voluntary or involuntary for somatic nerves?

Control is voluntary

Two types of somatic nerves?

motor and sensory nerves

Two types of nerve cells?

Glial cells, neurons.

Glial cells are _______

non-conducting

Function of Glial cells?

structural support, nourishment and regulates extracellular fluid.

Example of glial cells

Schwann cells

Neurons are _______

the functional unit of the nervous system

What do neurons carry?

tiny electric charges

Three types of neurons?

sensory, motor, interneurons

Function of sensory neurons?

transmit info from receptors to the CNS

Where is the cell body of sensory neurons located?

near the middle of the cell

Function of interneurons? Where are they located?

Analyze and interpret info from sensory neurons, sends info to motor neurons. Located only in the CNS.

Function of motor neurons?

relays info to effectors (muscles or glands)

Four parts of the neuron?

Dendrites, cell body, axon, axon terminal

What are dendrites?

extensions of the cell body

Function of dendrites?

receive info from other neurons or from receptors. conducts impulses toward cell body

What does the cell body contain?

nucleus and organelles and cytoplasm

Function of axons?

transmits electrical impulses towards neurons or effectors.

What does the diameter of an axon affect?

Speed of transmission

the axon terminal is the _________

end of the axon.

Nerve impulses travel in one way only. Which way do they travel?

Dendrite —> Cell body —> Axon

Axons are covered by _______

the myelin sheath (fatty protein)

What produces myelin?

Schwann cells and oligodendrocytes

Two functions of the myelin sheath?

Insulate the axon, speeds transmission

What are the areas between the myelin sheath/schwann cells called?

Nodes of ranvier

What do nodes of ranvier contain? And what do they generate?

contains ion gates, generates action potentials.

What is saltatory conduction?

It is how nerve impulses are transmitted in a myelinated axon.

What is a nerve impulse? What are they generated by?

Nerve impulses are the flow of ions. They are generated by action potentials.

What is the reflex arc?

It is the simplest neural pathway, it is involuntary (doesn’t require any brain coordination).

Five parts of the reflex arc in order?

Sensory receptor, sensory neuron, interneuron, motor neuron, effector

Spinal cord injury

unable to transmit info to somatic nerves

Can you repair nerves in your CNS?

norp but hypothermia is induced to slow cell damage

What helps repair nerves in the PNS?

neurilema

What is the neurilema?

It is a delicate membrane covering myelin and promotes the regeneration of damaged axons.

Multiple sclerosis

Myelin sheath of motor neurons is destroyed. Transmission of ions is slow

Parkinson’s

caused decrease in dopamine, motor neurons are not stimulated and cerebellum degenerates.

Alzheimer’s

decrease in acetylcholine (a neurotransmitter). no excitation of postsynaptic neuron. characterized by a loss of memory. The brain appears to have tangles which are beta amyloid (protein) deposits. The tangles choke and kill neurons.

What is membrane potential?

Is the potential difference across a plasma membrane

How is membrane potential formed?

by the distribution of ions

Charge at rest and when excited?

-70mV at rest, +40mV when excited

Resting Potential (Polarization)

voltage at rest, there is a higher concentration of Na+ outside the cell and K+ in the membrane. Nerve cell is not being stimulated. K+ leaks out of the cell slowly and negative ions and amino acids are trapped inside. Na+ closed, K+ open.

Action potential are ________

nerve impulses and are an all or none response

Depolarization

Neurotransmitters depolarize the membrane. Occurs when the threshold level is reached. Electrical impulse is sent down the axon and the inside of the axon becomes more positive. Sodium rushes into the cell and the rapid inflow reverses the the charge. Na+ open, K+ is closed

Repolarizaton

Restoring the membrane to its original charge. Na+ closed, K+ open.

Hyperpolarization

Also called the refractory period. Action potential cannot be initiated. Caused by inactivation of the Na+ gates, K+ channels are slow to close. Membrane potential becomes more negative than it was originally. membrane must be polarized or the neuron will not fire.

movement of action potential

impulse occurs by saltatory conduction, never moves backwards.

Threshold level

minimum amount of stimulus to elicit an action potential, neuron will not fire if threshold is not reached

Two ways to detect the intensity of the stimulus

1. the number of neurons excited

2. The frequency of impulses

What is synaptic transmission?

Is how neurons communicate. Chemical signal diffuses over a gap called a synapse (which involve a number of neurons)

How does synaptic transmission work?

1. Inside the presynaptic neuron: impulse causes vesicle to move (with the help of calcium) to the endplate and releases neurotransmitters

2. In the Synapse: neurotransmitters diffuse and are broken down by enzymes

3. At the postsynaptic neuron: neurotransmitters bind to receptors and cause either depolarization or hyperpolarization

What are neurotransmitters and what are they used for?

They are chemical messages that are used to communicate with other neurons and must bind to postsynaptic neurons to elicit a response.

Neurotransmitters can be either _____

excitatory or inhibitory

Excitatory neurotransmitters

cause Na+ gates to open and depolarizes the neuron

Inhibitory neurotransmitters

cause K+ gates to open and neuron is hyperpolarized

Three neurotransmitters?

Serotonin, dopamine, acetylcholine

Serotonin

Regulates mood, is produced at night to elicit sleep and is converted to melatonin.

Dopamine

role in movement and pleasure. high amounts cause feeling of pleasure. Low amounts cause parkinson’s and depression

Acetylcholine

excitatory effect with skeletal muscles. Too little leads to Alzheimer’s. It is broken down by cholinesterase.

Cholinesterase

Is an enzyme in the synapse and destroys acetylcholine

Response time of neurotransmitters

slow due to diffusion. more synapses = slower response

What is summation?

Means it takes two or more neurons firing to get a response.

What is the CNS protected by?

Skull, meninges and cerebrospinal fluid

Meninges

protective membrane that surrounds the brain, consists of three sublayers. Infection in these layers results in meningitis

Cerebrospinal fluid

Fills the space between the meninges and through the spinal cord

Functions of cerebrospinal fluid?

1. shock absorber

2. carries nutrients to brain cells

3. removes wastes

Function of the spinal cord?

takes sensory information to the brain, and motor messages from the brain to the effectors.

What does the spinal cord consist of ?

white and grey matter

What are the two nerve tracts that the nerves connected to the spinal cord are organized into?

Dorsal and ventral root

Three main sections of the brain

forebrain, midbrain, hindbrain

What does the forebrain consist of?

Cerebrum, thalamus, hypothalamus, olfactory lobe

cerebrum

largest part of the forebrain, surface is called the cerebral cortex. consists of two hemispheres that are connected by the corpus callosum.

functions of the cerebrum

behaviour, senses, movement, intellect, and memory

4 lobes of the cerebrum

1. frontal

2. temporal

3. parietal

4. occipital

What does the frontal lobe contain?

motor cortex and prefrontal cortex

pre frontal cortex functions

linked to intellect, decision making, personality, and short term memory

motor cortex controls…

movement of muscles e.g. walking, speech

temporal lobe

hearing, long term memory

parietal lobe contains…

contains the sensory cortex

parietal lobe interprets…

temperature, pain and touch (also linked to awareness, emotions and speech interpretation)

occipital lobe

interprets visual information

Thalamus

acts as a relay station, directs sensory info to cerebrum

Hypothalamus

plays a large role in maintaining homeostasis. connects to the pituitary gland

olfactory lobe

receives and interprets info about smell

Midbrain

located below the thalamus, relay center for some eye and ear reflexes

3 parts of hindbrain?

1. cerebellum

2. pons

3. medulla oblongata

cerebellum

controls coordination of limb movement, balance and muscle tone