Neurons and Neurotransmitters

Introduction to the Nervous System

Nervous System Can be divided into 2 Groups:

• Central Nervous System (CNS)

• Peripheral Nervous System (PNS)

Functions of the Nervous System

• Feeling

• Thinking

• Moving

• Awareness

• Coordination of body functions

• Homeostasis

• Responsiveness to changes

Introduction to the Nervous System 2

• Main cell types are neurons

• Neurons transmit impulses along nerve fibers to other neurons

• Neurons typically have: a cell body, an axon, and dendrites

• Nerves are bundles of axons

• Synapses are small spaces between cells

• Neurotransmitters: chemical messengers

General Functions of the Nervous System

• Integrative function: Impulses are conducted into the CNS from peripheral neurons where they come together to create sensations, memories, or thoughts that are converted into perception

• Conscious or Unconscious decisions follow; then impulses are conducted along peripheral neurons to the effectors.

• Effectors are muscles or glands that perform actions in response.

• This is the motor function of the nervous system

General Functions cont.

• Motor function can be divided into two groups

• 1. Somatic Nervous System: Voluntary-Skeletal muscles

• 2. Autonomic Nervous System: Involuntary- Cardiac and smooth muscle groups.

Multiple Choice

Which group controls the skeletal muscles?

• Somatic nervous system

• autonomic nervous system

Multiple Choice

Which is under voluntary control?

• Somatic nervous system

• autonomic nervous system

Multiple Choice

Which controls cardiac muscle, smooth muscle and glands?

• Somatic nervous system

• autonomic nervous system

Neurons

• Transmit impulses

• Have a cell body, axon, and dendrites

• Nerves are bundles of axons

• Synapse: Neurons communicate with other neurons at a small gap called the synapse

• Neurotransmitters are chemical messengers that propagate impulses to another cell

Neuron Structure

• Dendrites: conduct impulses to cell body; short and branching, and provide a receptive surface for communication with other neurons

• Axon: conduct impulses away from the cell body; arise from the axon hillock

• Cell body: mitochondria, lysosomes, golgi bodies, nissl bodies (R ER), neurofilaments, nucleus with a nucleolus

Open Ended

The 3 main parts of a neuron are

Myelinated and Unmyelinated Axons

• Large Diameter axons are myelinated; Smallest axons are not

• CNS- White matter - myelinated axons; CNS-grey matter- cell bodies and unmyelinated axons

Multiple Choice

Large axons are

• myelinated

• unmyelinated

Multiple Choice

The outer layer of myelin is surrounded by the

• cytoplasm

• node of ranvier

• neurilemma

• cell body

Multiple Choice

Narrow gaps in the myelin sheath between Schwann cells are called

• neurilemma

• dendrites

• sarcolemma

• nodes of Ranvier

Multiple Select

Grey matter of the CNS is made of which of the following

• myelinated axons

• cell bodies

• cytoplasm

• unmyelinated axons

Regeneration of Neurons

• Damaged PNS are able to regenerate their axons because the neurilemma of their Schwann cells help guide the growing axon to its original checkpoint

• CNS axons are myelinated by oligodendrocytes which lack a neurilemma so they do not regenerate

• Neural Stem cells in the hippocampus and near the ventricles of the brain can divide to produce new neurons or neuroglia in certain chemical environments

Multiple Choice

CNS axons can regenerate

• true

• false

Multiple Choice

PNS neurons are able to regenerate because they have a neurilemma

• true

• false

Classification of Neurons

• Multipolar: Many dendrites and one axon

• Bipolar: 2 processes extending from the cell body- an axon and a dendrite

• Unipolar: 1 process extending from their cell body that splits where one acts as an axon extending to the PNS and the other which enters the CNS

Multiple Choice

Neuron with 2 processes- an axon and 1 dendrite is

• Multipolar

• Bipolar

• Unipolar

Multiple Choice

Neuron with one axon and many dendrites is

• Multipolar

• Bipolar

• Unipolar

Multiple Choice

Neurons with only one process are

• Multipolar

• Bipolar

• Unipolar

Multiple Choice

What type of neuron is this?

• Multipolar

• Bipolar

• Unipolar

Multiple Choice

What type of neuron is this?

• Multipolar

• Bipolar

• Unipolar

Multiple Choice

What type of neuron is this?

• Multipolar

• Bipolar

• Unipolar

Neuroglia

• absolutely necessary for the survival of neurons

• They: fill spaces, support neurons, produce myelin, nourish neurons, and carry out phagocytosis

• They have the ability to divide, while neurons usually cannot.

Neuroglia: Cells that provide:

• nutrients

• insulation

• physical support

Neuroglia of the CNS

• Microglia: phagocytic cells

• Oligodendrocytes: form myelin sheaths around axons

• Astrocytes: structural support, regulation of ion and nutrient concentrations, blood-brain barrier

• Ependymal cells: line ventricles and cover choroid plexus within the ventricles

Neuroglia of the PNS

• Schwann cells: myelin producing neuroglia of the PNS

Multiple Choice

Which neuroglial cell is not found in the CNS?

• microglia

• schwann cells

• oligodendrocytes

• ependymal cells

• Astrocytes

Multiple Choice

Which of the neuroglial cells is important in protecting the CNS from infection?

• astrocytes

• microglia

• ependymal cells

• oligodendrocytes

• Schwann cells

Multiple Choice

Which of the neuroglial cells produces myelin in the CNS?

• microglia

• ependymal cells

• Schwann cells

• astrocytes

• oligodendrocytes

Synapses

• Junction between 2 communicating neurons

• Similar to a neuromuscular junction

• Gap between neurons is a synaptic cleft

• Sending neuron-presynaptic neuron

• receiving neuron-postsynaptic neuron

Synapses cont.

• neurotransmitter: chemical communication between neurons released at the synaptic knob

• receptors on the postsynaptic neuron receive neurotransmitter from the synaptic knob