CH 12 Nervous Tissue Overview

These flashcards cover key concepts related to nervous tissue, including neuron structure, functions, neural classification, and synaptic transmission.

What are the major divisions of the nervous system?

Central nervous system (CNS) and Peripheral nervous system (PNS).

What makes up gray matter in the nervous system?

Gray matter consists of cell bodies, unmyelinated axons, dendrites, and glia.

What is the primary function of neurons?

To conduct information throughout the nervous system.

List the types of neuroglia in the CNS.

Astrocytes, oligodendrocytes, ependymal cells, microglial cells.

What is the role of astrocytes?

They provide support, form the blood-brain barrier, and maintain the chemical environment.

How do sensory neurons function within the nervous system?

They send information from the PNS to the CNS.

What are the two divisions of the Autonomic Nervous System?

Sympathetic division and Parasympathetic division.

What is the resting membrane potential of a neuron?

Approximately -70 mV.

What happens during depolarization of the neuron?

Sodium channels open, sodium ions rush into the cell, making the inside less negative.

What initiates an action potential in a neuron?

Voltage-gated sodium channels open at threshold (-55 mV).

What is the function of the sodium-potassium pump?

It maintains ion gradients by pumping sodium out and potassium into the cell.

What are the components of a typical multipolar neuron?

Dendrites, soma (body), axon, and axon terminal.

What are the properties of action potentials?

Rapid changes in membrane potential that propagate along the axon.

What types of neurons are classified as afferent?

Sensory neurons that send information from sensory receptors to the CNS.

What are the characteristics of glial cells?

They support neurons, do not conduct action potentials, and can undergo mitosis.

Describe the differences between white matter and gray matter.

White matter is made of myelinated axons; gray matter contains cell bodies and unmyelinated axons.

What role do Schwann cells play in the nervous system?

They myelinate axons in the PNS.

How do electrical impulses travel in neurons?

Through action potentials generated by changes in membrane permeability.

Define leak channels in the context of neuronal communication.

They randomly open to allow ions to flow across the membrane, contributing to resting potential.

What is synaptic transmission?

The process by which neurons communicate through chemical signals across synapses.

What is the first step of chemical synaptic transmission?

The arrival of an action potential at the presynaptic membrane.

How are neurotransmitters related to synaptic transmission?

They are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron.

What is hyperpolarization?

A change in membrane potential making the inside more negative than the resting potential.

What effect do inhibitory synapses have on a neuron?

They make the postsynaptic neuron less likely to fire an action potential.

What happens during the repolarization phase of an action potential?

Potassium channels open and potassium ions exit the neuron, restoring negative internal charge.

What triggers the action potential to propagate along the axon?

The opening of voltage-gated ion channels in response to depolarization.

Name one common excitatory neurotransmitter.

Acetylcholine (ACh).

Which type of neuron typically has one axon and multiple dendrites?

Multipolar neuron.

How does myelin affect action potentials?

Myelin increases the speed of action potential propagation via saltatory conduction.

What is the all-or-none principle in action potentials?

Once the threshold is reached, an action potential occurs; if not, it does not happen.

What happens at the 'peak' of an action potential?

Voltage-gated sodium channels close and potassium channels begin to open.

Explain the significance of the refractory period.

It ensures that action potentials only travel in one direction and limits the rate of firing.

What is the role of neurotransmitter receptors in postsynaptic cells?

They convert chemical signals back into electrical signals.

What is the effect of the autonomic nervous system on internal organs?

It regulates involuntary functions such as heart rate and digestion.

Define the term 'interneuron' in the nervous system.

Neurons that process information within the CNS and connect sensory and motor neurons.

What type of glial cell is responsible for producing cerebrospinal fluid?

Ependymal cells.

Describe what happens during the threshold phase.

Sodium channels open, leading to depolarization if the membrane reaches -55mV.

What is the significance of the Nodes of Ranvier?

They are gaps in the myelin sheath critical for the propagation of action potentials.

Which ion primarily causes depolarization in neurons?

Sodium (Na+).

What type of synapses typically have excitatory effects?

Chemical synapses, particularly where neurotransmitters like glutamate are involved.

What happens during the 'resting state' of a neuron?

The neuron is polarized with a negative internal charge and a maintained concentration gradient.

What are the anatomical (structural) divisions of the nervous system?

The Central Nervous System (CNS) consists of the brain and spinal cord, while the Peripheral Nervous System (PNS) includes all nervous tissue outside the CNS (nerves, ganglia, peripheral receptors).

What are the functional divisions of the nervous system?

The Sensory (afferent) division carries sensory information toward the CNS from receptors, and the Motor (efferent) division carries commands from the CNS to effectors (muscles, glands).

What are the subdivisions within the motor (efferent) division of the nervous system?

1. Somatic nervous system: Voluntary control over skeletal muscles.2. Autonomic nervous system (ANS): Involuntary control over internal organs (smooth muscle, cardiac muscle, glands), further divided into sympathetic and parasympathetic divisions.3. Enteric nervous system: A 'mini-network' in the digestive tract walls, capable of some independent function.

What are the primary functions of gray matter?

Gray matter is where synapses, processing, and integration of signals occur due to the presence of neuronal cell bodies, dendrites, unmyelinated axons, and neuroglia.

What are the primary functions of white matter?

White matter's main function is fast conduction and long-distance communication between brain regions and to/from the spinal cord, due to its composition of mostly myelinated axons.

What is the order of signal flow through a multipolar neuron?

Dendrites (receive input) $\rightarrow$ Cell body (soma / perikaryon / axon hillock region) $\rightarrow$ Axon (initial segment $\rightarrow$ myelinated segments/nodes $\rightarrow$ axon terminals / synaptic terminals / synaptic boutons) $\rightarrow$ Synapse.

What is the role of oligodendrocytes in the CNS?

Oligodendrocytes form myelin sheaths around axons within the CNS, covering multiple segments on multiple axons.

What is the role of microglial cells in the CNS?

Microglial cells serve as the immune defense in the CNS, performing phagocytosis of debris and assisting in injury response.

What is the role of ependymal cells in the CNS?

Ependymal cells line the ventricles of the brain and the central canal of the spinal cord, and they help produce and circulate cerebrospinal fluid (CSF).

What is the role of satellite cells in the PNS?

Satellite cells surround neuron cell bodies in ganglia, regulating the environment, providing support, and maintaining ion balance.

What is sensation (sensory input) in the nervous system?

Sensation is the process of detecting changes in the internal or external environment via receptors and sending that information to the CNS.

What is integration in the context of nervous system function?

Integration is the processing and interpreting of sensory input, combining it with memory, emotions, and past experience to decide on an appropriate action.

What is response (motor output / effect) in the nervous system?

Response is the sending of signals from the CNS via motor neurons to effectors (muscles, glands) to produce a specific action, such as movement or secretion.

What are the key components of the membrane that establish the resting membrane potential?

1. The lipid bilayer (impermeable to many ions)
2. Ion channels (especially 'leak' channels for K$^+$ and Na$^+$)
3. The Na$^+$/K$^+$ ATPase pump (pumps 3 Na$^+$ out, 2 K$^+$ in)
4. Unequal distribution of ions (higher [K$^+$] inside, higher [Na$^+$] outside)
5. Selective permeability (more permeable to K$^+$ than Na$^+$ via leak channels)
6. Electrochemical gradients.

Describe the phases of an action potential in sequence.

1. Resting state: Membrane at $\approx -70$ mV, most channels closed.
2. Depolarization to threshold: Stimulus causes depolarization; at $\approx -55$ mV, voltage-gated Na$^+$ channels open.
3. Rising phase (rapid depolarization): Na$^+$ rushes in, membrane potential becomes positive.
4. Peak / overshoot: Na$^+$ channels inactivate, membrane potential may go above $0$ mV.
5. Repolarization: Voltage-gated K$^+$ channels open, K$^+$ flows out, potential returns to negative.
6. Hyperpolarization (undershoot): More K$^+$ exits than needed, membrane goes slightly more negative than resting.
7. Return to resting potential: K$^+$ channels close, Na$^+$/K$^+$ pump and leak channels restore ion distributions.