Anatomy - nervous system & the brain

Central nervous system

Brain & spinal chord

Peripheral nervous system

Connects the CNS to the rest of the body

Sensory division

Afferent; nerve fibers that carry information to the CNS

Motor division

Efferent; nerve fibers carry impulses away from CNS

Somatic nervous system

1 of 2 efferent divisions; voluntary

Autonomic nervous system

1 of 2 efferent divisions; involuntary

Neurons

Nerve cells specialized to transmit messages

Cell body

Nucleus & metabolic center of the cell

Dendrites

Conduct impulses toward cell body

Axons

Conduct impulses away from the cell body; covered in myelin sheath

Myelin sheath

Covers axons; insulates & protects, allowing for faster communication

Nodes of ranvier

Where the axon is exposed allowing for Na+ and K+ out, regenerating electrical signal, preventing it from weakening

Multipolar neurons

Many extensions from the cell body; most neurons are of this type

Bipolar neuron

One axon and one dendrite

Unipolar neurons

Have a short single process leaving the cell body

Glial cells

Provide structural support, insulation, nourishment, waste removal, and immune system support

Oligodendrocytes

Type of support cell; produce myelin sheath around nerve fibers in CNS

Satellite cells

Type of support cell; protect neuron cell bodies

Schwann cells

Type of support cell; form myelin sheath in PNS

Axonal terminals

Ending of axons containing vesicles with neurotransmitters. Release a neurotransmitter that acts on a dendrite

Synapse

Junction between the nerves; separated by the synaptic cleft

What type of impulses do sensory neurons carry?

Impulses from sensory organs

What type of impulses do motor neurons carry?

Impulses from CNS

Intermediate (relay) neuron

In the CNS; connect sensory and motor neurons

Irritability

Ability to respond to stimuli

Conductivity

Ability to transmit an impulse

Polarized

The plasma membrane at rest; fewer positive ions are inside the cell than outside of it

Depolarization

A stimulus depolarizes the neuron’s membrane, allowing Na+ to flow inside the membrane

What initiates the action potential in a neuron?

The exchange of ions

Action potential

Nerve impulse

Re-polarization

Potassium ions rush out of the neuron after sodium ions rush in

Sodium-potassium pump

Restores original configuration of neuron & requires ATP

Where in action potential started?

In the dendrite

Epidural

Regional anesthesia in which medication is injected into the epidural space (area surrounding spinal cord), which blocks pain signals while allowing for some movement/sensation

Reflex

Rapid, predictable & involuntary responses to stimuli

Reflex arc

Direct route from a sensory neuron, to an interneuron, to an effector. Bypasses the brain & protects us from harm, maintains balance

Autonomic reflexes

Smooth muscle regulation, heart/blood pressure regulation, regulation of glands & digestive system

Somatic reflexes

Activation of skeletal muscles

Where does the CNS develop from?

Embryonic neural tube; neural tube becomes brain & spinal cord

4 regions of the brain

Cerebral hemispheres, diencephalon, brain stem, and cerebellum

Cerebral hemispheres

Includes more than half of brain mass; paired (left & right) superior parts of the brain

Gyri

Ridges; make up cerebrum surface

Sulci

Grooves; make up cerebrum surface

Fissures

Deep sulcus

Frontal lobe

Largest and most complex; in charge of executive functioning, higher order intellectual functions, personality, memory, attention & concentration, emotion & social behavior, and primary motor cortex

Broca’s area

Speech production & articulation; located in the frontal lobe

Central sulcus

Separates frontal from parietal lobes

Anterior region

Part of central sulcus, processes motor information

Posterior region

Part of the central sulcus, organizes and processes sensory information

Parietal lobes

In charge of sensory inputs such as touch, vibration, pain temperature, etc.

Temporal lobes

Perception of auditory (sound) and olfactory (smell) information

Occipital lobes

Visual informatin interpretation

Insular lobes

Process of sending internal body states

Gustatory area

Taste

Gray matter

In charge of processing, memory, emotion, movement, and cognitive functions

What is within gray matter?

Mostly unmyelinated neurons & large number of neural bodies with nuclei for information processing

White matter

Connects different regions of the brain allowing for information exchange

Corpus callosum

Connects right and left parts of the brain, allowing them to work together

What is the left hemisphere associated with?

Logical thinking, language, and analytical skills

What is the right hemisphere associated with?

Creativity, spatial reasoning, and emotional processing

Diencephalon

Acts as a bridge between nervous and endocrine systems; made up of the thalamus, hypothalamus, and epithalamus

Where is the diencephalon located?

On top of the brain stem, & enclosed by cerebral hemispheres

Thalamus

Relay station for sensory impulses. Transfers impulses to the correct part of the cortex for localization and interpretation

Hypothalamus

Important autonomic nervous system center that controls various unconscious functions needed for survival (temperature, hunger, thirst, & breathing)

Limbic system

Emotions

What is the hypothalamus a part of?

The limbic system & processes and responds to fear, anger, stress; control of the endocrine system

What is attached to the hypothalamus?

Pituitary gland

Epithalamus

Houses the pineal body (endocrine gland)

Brainstem

Links brain to spinal cord; made up of midbrain, pons, & medulla

Midbrain

Motor movement of eye; relay center for vision & hearing and skeletal movement.

What is Parkinson’s caused by?

The destruction of dopamine producing neurons deep in the midbrain

Pons

Unconscious jobs like breathing; coordinate face and eye movements. Relays information between forebrain and cerebellum

Medulla oblongata

Relay between brain and spinal cord; regulates basic autonomic functions, like breathing and swallowing

Cerebellum

Provides involuntary coordination of body movements; “little brain”

What is the cerebellum split into?

2 hemispheres with convoluted surfaces; split into posterior, inferior, underlying temporal, & occipital

Cerebrospinal fluid (CSF)

Surrounds brain & brainstem, cushions and protects

Choroid plexus

Produces CSF in 4 ventricles

Ventricles of the brain

Interconnected cavities; 2 lateral ventricles & 3rd and 4th

What are protections of the central nervous system?

Scalp & skin, skull & vertebral column, meninges, cerebrospinal fluid, blood brain barrier

Meninges

3 membranes to cover and protect the brain and spinal cord

Dura mater

First layer of the meninges; it is a double layer and the most superficial

Arachnoid

Middle layer of the meninges

Pia

Deepest layer of the meninges

Epidural, subdural, subarachnoid

Spaces between the layers of the meninges

Hemorrhage

Bleeding due to a damaged blood vessel

What are the types of hemorrhages?

Epidural hematoma, subdural hematoma, subarachnoid hemorrhage, intracerebral hemorrhage

Blood brain barrier

Endothelium cells that form the lining of blood vessel are packed more tightly together compared to other vessels in the body; protects against bacteria, viruses, or other toxins from entering the brain

Which substances can get through the blood brain barrier?

Fats and soluble molecules, respiratory gases, alcohol, nicotine, anesthesia

Spinal cord

Extends from the medulla to the region of L1-2

Cauda equina

Collection of spinal nerves

Where do enlargements in the spinal cord occur?

Cervical and lumbar regions; higher density of sensory & motor neurons

Nerve

Bundle of neuron fibers; neuron fibers bundled by connection tissue

What is in the central canal of the spinal cord?

Cerebrospinal fluid

Mixed nerves

Both sensory and motor fibers

Cranial nerves

12 pairs of nerves that mostly serve the head and back and originate from the brain stem

Spinal nerves

Formed by the combination of the central and dorsal roots in the spinal cord; come in pairs at the level of each vertebrae (total of 31 pairs)