Ch.11 Nervous System

Overview of Neuronal Processes

• Neuronal processes are vital extensions from the cell body of neurons, serving as conduits for signaling within the nervous system.

• There are two main types of neuronal processes: dendrites and axons.

Neurons

• Cell Body (Soma): Contains the nucleus and is where most metabolic activities occur.

• Process: Refers to the extensions that emerge from the neuron’s soma, primarily including dendrites and axons.

Types of Neurons

• Sensory Neurons: Primarily located in the peripheral nervous system, they carry signals from sensory receptors to the central nervous system (CNS).

• Motor Neurons: Carry signals from the CNS to muscles or glands, involved in movement.

• Association Neurons (Interneurons): Connect sensory and motor neurons, playing key roles in reflexes and neuronal processing.

Neuronal Processes

Dendrites

• Function: Dendrites receive incoming signals.

• Structure: Often branched and covered with dendritic spines, which enhance the surface area for signal reception.

• Dynamic Nature: Dendrites can change in structure in response to stimulation (neuroplasticity).

Axons

• Function: Transmit signals away from the cell body.

• Structure: Generally longer than dendrites; can be myelinated or unmyelinated.

• Axon Hillock: The cone-shaped area of the axon that generates action potentials.

• Terminals: The endpoint of axons where neurotransmitters are released.

Neural Communication

• Neurotransmitters: Chemicals released from the axon terminals into the synaptic cleft, responsible for signaling between neurons.

• Signal Transmission: Happens through the generation of action potentials along the axon, triggered by depolarization processes.

Mechanisms of Action Potentials

1. Resting Potential: The neuron at -70 mV, stable and inactive.

2. Depolarization: Sodium channels open, causing a rapid increase towards +30 mV.

3. Repolarization: Potassium channels open, bringing voltage back down to reset.

4. Hyperpolarization: The membrane potential becomes more negative than resting potential due to prolonged potassium channel activity.

Myelination

• Myelin Sheath: Fatty insulation around axons that speeds up signal transmission.

• Nodes of Ranvier: Gaps in the myelin sheath that facilitate rapid saltatory conduction of impulses.

• Importance: Myelination is crucial for quick responses in emergency situations (e.g., sympathetic responses triggered by danger).

Neuroglia (Supporting Cells)

• Astrocytes: Maintain blood-brain barrier and supply nutrients to neurons.

• Oligodendrocytes: Form myelin in the central nervous system.

• Microglia: Act as immune defense in the nervous system.

• Ependymal Cells: Line the cavities and produce cerebrospinal fluid.

White Matter vs. Gray Matter

• White Matter: Composed of myelinated axons (tracks in the CNS).

• Gray Matter: Composed mainly of neuronal cell bodies and unmyelinated fibers (nuclei in the CNS).

Emotional Impact of Neural Function

• Neurotransmitters influence emotions and mental health.

• Issues such as anxiety and depression can be linked to the functioning of neurotransmitters and the health of neural connections.

• Sympathetic vs. Parasympathetic Responses: Fast reactions (fight or flight) vs. slow reactions (rest and digest) driven by the type of signals processed by the neurons.

Importance of Balance in Neural Functioning

• The balance of neurotransmitters is crucial to maintaining emotional health and stability.

• Negative emotions can result from imbalances in neural activity, often necessitating professional help or therapy.