Nervous system flashcards

(CH13-18)

Nervous system

Organ system that monitors:

• stimuli

• integrates information

• produces responses

Three main functions of the nervous system

1. Monitor: Sensory receptors detect changes (stimuli) both inside and outside the body

2. integrate: The central nervous system (brain and spinal cord) receives, processes, and interprets the incoming sensory data.

3. respond: The nervous system sends signals out to effectors (muscles or glands) to produce a physical or chemical reaction.

Central nervous system (CNS)

Consists of the brain and spinal cord

Peripheral nervous system (PNS)

Consists of nervous tissue outside the brain and spinal cord including nerves and ganglia

Afferent division

Sensory division that carries information through the PNS toward the CNS

Ascending pathway carries sensory information toward higher levels of the CNS

Example: You touch a hot stove.

1. Sensory receptors in your skin detect the heat.

2. Afferent neurons carry the sensory signal toward your spinal cord.

3. Your CNS receives the information and processes it.

Other examples include feeling pain, detecting pressure, and sensing temperature.

Efferent division

Motor division that carries information away from the CNS, through the PNS to effectors

Descending pathway carries motor information toward lower levels of the CNS

Example: You pull your hand away from the hot stove.

1. Your CNS processes the sensory information.

2. Efferent neurons carry a motor command away from the CNS.

3. Your arm muscles contract, pulling your hand away.

Efferent signals can control voluntary movements, such as raising your arm, or involuntary functions, such as changing your heart rate.

Sensory neuron

Neuron that conducts impulses toward the CNS

Sensory neurons tell your brain and spinal cord what is happening inside and outside your body. (hot stove)

Most sensory neurons are pseudounipolar neurons

Apart of Afferent division

Motor neuron

Neuron that conducts impulses away from the CNS

Effectors include muscles and glands. Motor signals can produce skeletal muscle contraction, regulate internal muscle activity, or stimulate glandular secretion.

Most motor neurons are multipolar neurons

Apart of Efferent division

Interneuron

Association neuron located in the CNS that connects and processes information between neurons

They are important for integrating sensory information, coordinating responses, and participating in neural circuits involved in learning and other complex functions.

Most interneurons are multipolar neurons

Somatic nervous system (SNS)

Apart of Efferent division (PNS)

Primarily voluntary, controls skeletal muscles

Autonomic nervous system (ANS)

Apart of Efferent division (PNS)

Primarily involuntary, regulates smooth muscle, cardiac muscle, and glands

Sympathetic nervous system

Autonomic division associated with Preparing your body for stress or activity.

fight, flight, or freeze

Parasympathetic nervous system

Autonomic division associated with Supporting recovery, digestion, and energy conservation.

rest and digest

Effectors

Muscles or glands that respond to motor signals

How are sensory inputs and motor outputs classified?

• Somatic: Relates to the body wall and limbs, including the skin, skeletal muscles, and joints.

• Visceral: Relates to the internal organs, such as the heart, lungs, stomach, and intestines.

• General: Sensory information detected by receptors widely distributed throughout the body, such as touch, pressure, pain, and temperature.

• Special: Sensory information detected by localized, specialized sensory organs, including vision, hearing, taste, smell, and equilibrium (balance).

• Proprioception: Awareness of body position and movement through sensory information from muscles, tendons, and joints.

• Branchial motor innervation: Motor nerve supply to skeletal muscles derived from the pharyngeal (brachial) muscle, including certain muscles of the face, jaw, throat, and neck.

Dorsal sensory ventral motor rule

Sensory information enters the spinal cord through dorsal roots

and motor information exits through ventral roots

Somatic vs visceral

Somatic refers to the body wall and limbs while visceral refers to internal organs

General vs special senses

General senses include touch, pressure, pain, and temperature

while special senses include vision, hearing, taste, smell, and equilibrium

Nerve

Bundle of axons in the PNS

Tract

Bundle of axons in the CNS

Ganglion

Cluster of neuron cell bodies in the PNS

Nucleus in neuroanatomy

Collection of neuron cell bodies in the CNS

Spinal nerves

Spinal nerves are part of the PNS and are all mixed nerves,

meaning they contain both sensory (afferent) and motor (efferent) fibers.

Neuron

Functional cell of nervous tissue that receives and transmits information

Three main parts of a neuron

1. Dendrites

2. cell body or soma

3. axon

Soma

Neuron cell body containing the nucleus and most organelles

Dendrites

Branched processes that usually receive information toward the cell body

Axon

Neuron process that carries nerve impulses away from the cell body

Axon hillock (axon features)

Region where the axon emerges from the cell body

Axon terminals or terminal boutons (axon features)

Endings of an axon involved in communication with other cells

Nissl bodies (chromatophilic substance)

Rough endoplasmic reticulum and ribosomes involved in protein synthesis

Synapse

Junction where a neuron communicates with another cell

Neurotransmitter

Chemical messenger released by a neuron that binds to receptors on a target cell

Chemical synapse

Junction where neurotransmitters cross a synaptic cleft to communicate with another cell

Electrical synapse

Junction that transmits signals directly between cells through gap junctions

Synaptic cleft

Small gap between the presynaptic and postsynaptic cells

Chemical synapse sequence

Electrical impulse reaches the axon terminal

neurotransmitter is released

target cell receives the signal through receptors

Note:

Action potential is the electrical impulse traveling along a neuron membrane

Multipolar neuron

Neuron with several dendrites and one axon

common in the brain and spinal cord

Bipolar neuron

Neuron with one dendrite and one axon

associated with specialized sensory pathways

Pseudounipolar neuron

Sensory neuron with one process that divides into two branches

Unipolar and Pseudounipolar neurons are most sensory nerves in the body

Neuroglia (glial cells)

Supporting cells that protect, nourish, regulate, and insulate neurons

Four CNS neuroglia

1. Astrocytes: Support neurons and help maintain the blood-brain barrier.

2. microglia: Remove pathogens and cellular debris by phagocytosis.

3. ependymal cells: Line CNS cavities and help produce and circulate cerebrospinal fluid.

4. oligodendrocytes: Form myelin sheaths around CNS axons.

Two PNS neuroglia

1. Schwann cells: Myelinate PNS axons and help with nerve repair.

2. satellite cells: Surround neuron cell bodies in ganglia and maintain their environment.

Astrocytes

Star-shaped CNS glial cells that support neurons and help maintain the blood-brain barrier

Blood-brain barrier (BBB)

Selective barrier regulating movement of substances from blood into CNS tissue

Special feature: Tight junctions between brain capillary endothelial cells that help form barrier

Microglia

CNS immune cells that remove debris and foreign material through phagocytosis (Engulfing and digesting unwanted material)

Phagocytosis

Ependymal cells

CNS glial cells that line brain ventricles and the spinal cord central canal and help produce and circulate CSF

Cerebrospinal fluid (CSF)

Fluid that surrounds and cushions the brain and spinal cord

helps nourish the brain and removes wastes

transmits neurotransmitters around CNS

CSF is mostly made in the CHOROID PLEXUS

Oligodendrocytes

CNS glial cells that form myelin around segments of multiple axons

Schwann cells

PNS glial cells that form myelin around individual axon segments and assist peripheral nerve repair

Satellite cells

PNS glial cells that surround neuron cell bodies in ganglia

Myelin sheath

Insulating layers around axons that increase conduction speed

Nodes of Ranvier

Gaps between myelin sheath segments

Saltatory conduction

When a nerve signal quickly jumps from one node of Ranvier to the next along a myelinated axon.

Dorsal root

Carries sensory information into the spinal cord

Ventral root

Carries motor information out of the spinal cord

Reflex

Rapid automatic response to a stimulus either somatic or visceral

Reflex arc

Neural pathway responsible for a reflex response

There are two types:

Monosynaptic reflex arc: Reflex pathway with one synapse directly connecting a sensory neuron and a motor neuron.

Polysynaptic reflex arc: Reflex pathway with one or more interneurons between sensory and motor neurons.

Five components of a reflex arc

1. Receptor

2. sensory neuron

3. integration center

4. motor neuron

5. effector

Unipolar Neuron

contains one process attaching to one body.

Unipolar and Pseudounipolar neurons are most sensory nerves in the body

Anaxonic neuron

Neuron with multiple processes but no clearly distinguishable axon

found in CNS

Main functions of the brain

1. Controls movement

2. interprets sensation

3. supports consciousness, cognition, and autonomic regulation

Four major brain regions

1. Cerebrum

2. diencephalon

3. brain stem

4. cerebellum

Cerebrum

Largest brain region with two hemispheres responsible for…

1. conscious sensation

2. movement

3. higher thought

Diencephalon

Region containing the…

• thalamus

• hypothalamus

• epithalamus

Brain stem

1. Midbrain

2. pons

3. medulla oblongata

Contains white matter tracts with internal gray matter nuclei

produces automatic behaviors

acts as passageway for all fiber tracts running from cerebrum to spinal cord

involved with innervation of head, 10 of 12 cranial nerves attached to the brain stem

Cerebellum

Two cerebellar hemispheres connected medially by the vermis

Two primary functions:

• Helps maintain posture and equilibrium

• fine-tunes voluntary and involuntary movements

Gray matter vs white matter

Gray matter contains mainly neuron cell bodies

while white matter contains mainly myelinated axons and bundled into large tracts

Cerebral cortex

superficial gray matter layer of the cerebrum

Basal nuclei

Internal structure of the cerebrum

Deep gray matter portion within the white matter involved in regulating movement

Frontal lobe

separated from the parietal lobe by the CENTRAL SULCUS

Voluntary movement and executive functions

Parietal lobe

Somatic sensation and spatial processing

Temporal lobe

Hearing, language, and memory

lateral side of the hemisphere

• separated from the parietal and frontal lobes by the LATERAL SULCUS

• inferiorly separated from the occipital lobe by the CALCARINE SULCUS

Occipital lobe

Vision

lies farthest posteriorly, separated from parietal lobe by the parieto-occipital sulcus occipital fissure

Insula

Deep region of the cerebral cortex within the lateral sulcus

involved in taste and visceral sensations (internal body sensations)

Central sulcus

Groove separating the frontal and parietal lobes

located between the precentral (motor) and postcentral (sensory) gyri

Lateral sulcus

Separates temporal lobe from frontal and parietal lobes

Gyrus vs sulcus

Gyrus is a raised fold, while sulcus is a groove

Primary motor cortex

Located in Precentral gyrus of frontal lobe

controls voluntary movement

• especially the forearms, fingers, and facial movements

Primary somatosensory cortex

Located in the postcentral gyrus of parietal lobe

Processes body sensations

• touch, pressure, pain, temperature, and body position

Contralateral cortical control

Each hemisphere primarily controls and senses the opposite body side

Motor vs sensory homunculus

Motor map is on precentral gyrus

sensory map is on postcentral gyrus

Somatotopy: the organized mapping of body parts onto the cerebral cortex.

Why are the hands and face large on the homunculi?

They require especially fine motor control or detailed sensory processing

• lips and hands are the most sensitive body parts

Premotor cortex

Plans and organizes more complex movements

anterior to precentral gyrus

Frontal eye field

Controls voluntary eye movements

anterior to the premotor cortex

Broca area vs Wernicke area

Broca supports movements necessary for speech production

Wernicke supports language comprehension

Both: Usually located in the left hemisphere, which is the language-dominant hemisphere for most people.

Primary visual cortex

Largest cortical sensory area.

Receives visual information originating from the retina of the eye.

Located on the medial surface of the occipital lobe along the calcarine sulcus;

Primary auditory cortex

responsible for conscious hearing

• loudness, rhythm, and pitch

Located in the superior temporal lobe primarily inside the lateral sulcus

Gustatory cortex

Taste processing, especially insular and nearby cortex

lies on roof of lateral sulcus

Olfactory cortex

Smell processing

media laspect of cerebrum in piriform lobe

Three cerebral white matter fiber types

1. Association fibers: Connect areas within the same cerebral hemisphere

2. Commissural fibers: Connect the left and right cerebral hemispheres.

3. Projection fibers: Connect the cerebral cortex to lower regions of the CNS

Association fibers

Connect regions within one hemisphere

run horizontally

Commissural fibers and corpus callosum

Commissural fibers connect the left and right cerebral hemispheres.

The corpus callosum is the largest bundle of commissural fibers

Projection fibers

Connect cerebral cortex with lower CNS regions

run vertically to and from brain stem and spinal cord

Thalamus

Major relay for sensory signals to the cortex

Hypothalamus

inferior portion of the diencephalon

Most important visceral control center

Regulates homeostasis, autonomic functions, and endocrine activity

• forms a link between the nervous and endocrine systems

Epithalamus

most dorsal part of diencephalon and includes the pineal gland

Pineal gland secretes melatonin involved in sleep-wake timing

Midbrain colliculi

Superior colliculi control visual reflexes

inferior colliculi control auditory reflexes

both form the Corpora quadregemina

Pons

between midbrain and medulla oblongata

Brain stem relay region that helps…

• regulate breathing

• To help coordinate involuntary skeletal muscle movements and muscle tone

• relaying information to and from the brain/spinal cord

Medulla oblongata

most caudal part of brainstem, directly connects brain with spinal cord

relay station for cranial nerve nuclei

controls important visceral functions such as…

• respiratory

• cardiovascular (heart rate and blood pressure)

• protective reflex centers