Neurobiology IV

Acetylcholine

• Nicotinic

  • Receptor type - ionotropic

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  • Receptor location - Skeletal muscles, autonomic neurons, CNS

  • Effect - Excitatory

• Muscarinic

  • Receptor Type - metabotropic

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  • Receptor location - Smooth and cardiac muscle, endocrine and exocrine glands, CNS

  • Effect - Excitatory and Inhibitory

Synthesis of Acetylcholine as a Neurotransmitter

Acetylcholine ( Cholinergic receptor) subtypes

Diversity of neurotransmitters

• Dopamine

  • Receptor - dopamine

  • receptor type - metabotropic

  • Receptor Location - CNS

  • Effect - Excitatory or inhibitory

• Norepinephrine

  • Receptor - a and B adnergic

  • receptor type - metabotropic

  • Receptor Location - CNS and PNS, cardiac muscle, smooth muscle

  • Effect - Excitatory or inhibitory

Norepinephrine receptor cause differing reponses

• Norepinephrine binds to several different receptor types

• Type depends on function

• a1 andrenergic receptor

  • cause vasoconstriction in smooth muscle

• a2 adrenergic receptor

  • inactivates calcium channels and reduce release of NE

• B1 receptor

  • activate calcium channels and increase muscle contraction in cardiac muscle

• B2 receptor

  • reduces muscle contraction and causes vasodilation

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• Some of the differing effects

  • pupil dialiation

  • stronger heart contraction

  • increase. non-shivering thermogenesis in brown adipose tissue

  • constrict arteries - increased BP

  • cause release of renin and Na+ in kidneys

  • increase glycogenolysis

  • increase release of glucagon

  • increase glucose uptake in skeletal muscles

  • increase lipolysis

  • reduce digestive activity in digestive system

Classes of Neurons

• Multipolar neurons

  • One process, called an axon, carries signals away from the cell body, while the other processes, called dendrites, receive signals from other neurons. Multipolar neurons are found in the brain and spinal cord, and they play a crucial role in transmitting and integrating information within the nervous system.

• Bipolar neuron

  • They have two distinct processes, or extensions, known as dendrites and axons. Dendrites receive signals from other neurons, while axons transmit signals to other neurons or target cells.

  • Bipolar neurons are commonly found in the retina of the eye, where they play a role in transmitting visual information. They are also present in the olfactory system, where they help in detecting and transmitting information about smells.

  • Overall, bipolar neurons are specialized for relaying sensory information in specific sensory pathways.

• Unipolar neuron ( afferent neurons)

  • A unipolar neuron, also known as a sensory neuron, is a type of neuron that has a single process extending from the cell body. This process acts as both the axon and the dendrite.

  • Unipolar neurons are primarily involved in transmitting sensory information from the periphery to the central nervous system. They are found in sensory ganglia, such as the dorsal root ganglia of the spinal cord, and have specialized receptors at their peripheral endings to detect various stimuli.

  • The information received by the unipolar neuron is then transmitted to other neurons in the central nervous system, allowing for the perception and interpretation of sensory stimuli.

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Functional classes of neurons

• Sensory neuron ( afferent neuron)

  • theses are considered unipolar neuron

  • trigger zone - interface between the dendrites and the axon

  • carry impulses from the periphery to the CNS

• Interneuron

  • connect one neuron to another

  • typically multipolar and may have multiple axon terminals

  • varying functional class

  • many dendrites

• Motor neuron (efferent neuron)

  • carry signal from the CNS to some external target organ - muscle and other tissues which are stimulates

  • generally multipolar

  • elicits a response in the effector organ

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Myelination increases the speed of AP conduction down the axon

• AP generation is slower than electronic spread

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• Electronic current decreases with distance while action potential maintain amplitude

• Myelin sheath insulates region of the axon

  • restricts action potentials to nodes of Ranvies

  • Forces electronic spread through the internodes

  • Best compromise between action potentials and electronic spread

• AP conduction speeds

  • heavily myelinated: 15-150 m/s

  • Lightly myelinated : 3 -15 m/s

  • Unmyelinated: 1 m/s

• Signals travel faster through the internodes than the nodes of Ranvier

• Larger diameter axons increase AP conduction speeds

• Neurons exhibit variation in the morphology of synapse

• Neuron to neuron synapses occur to a variety of locations

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