Nervous System

Development of the Nervous System

- begins as a tube along the axis of the body
- folds over during development and is hollow as a result
- starts as 3 swellings after 4 weeks in the uterus (turns into 5)
- neural tube becomes the spinal cord

Rhombencephalon

Hindbrain

Mesencephalon

Midbrain

Prosencephalon

Forebrain

spina bifida

when the neural tube doesn't completely close at the caudal end

Central Nervous System

- brain
- spinal cord

Peripheral Nervous System

- neural tissue outside of the CNS
- sensory and motor neurons

Sensory Nervous System

contains receptors that transmit information to the CNS

Motor Nervous System

- transmits information for the CNS to the rest of the body
- sends motor information to effectors

Somatic Sensory

- apart of the sensory nervous system
- voluntary actions

Visceral Sensory

- apart of the sensory nervous system
- involuntary actions

Somatic Motor

- apart of the motor nervous system
- voluntary actions

Autonomic Motor

- apart of the motor nervous system
- involuntary actions

Gray Matter

- consists of neural and glial cell bodies
- outer portion of the brain
- inner portion of the spinal cord

White Matter

- consists of axons
- inner portion of the brain
- outer portion of the spinal cord

Nerves

- cable like bundle of parallel axons
- surrounded by three layers of connective tissue

Endoneurium

delicate connective tissue around individual axons in nerve

Perineurium

the sheath of connective tissue that covers a bundle of nerve fibers (fascicles)

Epineurium

connective tissue surrounding the entire nerve

Synapse

- junction between two neurons that is responsible for unidirectional transmission of nerve impulses
- can make contact with cell bodies, dendrites or other axons
- release neurotransmitters

Excitatory

- type of synapse
- activity promotes impulses
- depolarizes the next cell membrane

Inhibitory

- type of synapse
- inhibits impulse transmission
- hyperpolarizes next cell membrane

Acetylcholine

- neurotransmitter that is released at all neuromuscular junctions

Multipolar Neuron

- has several dendrites
- one axon
- majority of the neurons in the CNS

Unipolar Neuron

- one long axon with dendrites at the end
- touch and stretching

Bipolar Neurons

- one dendrite and one axon
- makes up many sensory nerves

Pyramid Neuron

- type of multipolar neuron
- triangular shaped bodies
- found in the cerebral cortex, hippocampus and amygdala
- linked to cognitive ability

Neuroglia

- glial cells
- CNS and PNS
- physically protect and nourish the neuron
- higher amount compared to the amount of neurons

Oligodendrocytes

- CNS axons only
- extensions of cytoplasm that wrap around the axon
- produce myelin to insulate the electrical activity and produce rapid nerve impulses

Schwann Cells

- PNS only
- whole cell that wraps around an axon
- insulate electrical activity by myelinating the axons for rapid nerve impulses

Astrocytes

- most common glial cell
- regulation of the environment around axons and synapses
- repairs damage of neurons

Microglia

- type of macrophage associated with the immune system
- clean-up cell

Multiple Sclerosis

- results from the destruction of the myelin sheath and axons

Meninges

- three layers of connective tissue that surround the spinal cord and brain
- protection

Pia Mater

- innermost layer of meninges
- adheres to surfaces
- highly vascular

Arachnoid Mater

- middle layer of meninges
- weblike and avascular

Dura Mater

- outer layer of meninges
- dense, irregular connective tissue
- 2 layers in the brain

Epidural Space

- area between the vertebral column/cranium and dura mater
- blood vessels, fat and connective tissue

Subdural Space

- area between the arachnoid and dura mater
- contains interstitial fluid

Subarachnoid Space

- area between the pia and arachnoid mater
- contains cerebralspinal fluid

Severe Head Trauma Cases

- can create bleeding between the meninges
- cause pressure that can destroy neurons and glia cells

Epidural Block

- regional anesthesia that numbs the lower body

Spinal Tap

- needle inserted between the lumbar vertebrae into subarachnoid space
- withdraws cerebrospinal fluid and can introduce substances

Cerebrospinal Fluid

- produced in the choroid plexuses of each of the four brain ventricles
- found in the subarachnoid space of the brain and spinal cord
- protection of the brain; brain floats in it and provides cushioning
- transports nutrients and removes wastes

Hydrocephalus

- cerebrospinal fluid accumulates in the brain ventricles
- babies heads with swell

Blood-Brain Barrier

- barrier that strictly regulates which substances can enter the interstitial fluid in the brain
- capillaries in the brain are selectively permeable
- glial cells surround the capillaries to catch things that get through the barrier

Bone

- most important physical defense for the CNS
- not applicable for the PNS

Spinal Cord

- pathway for sensory and motor impulses to and from the brain
- responsible for the quickest reflex reactions to a stimulus

External Spinal Cord Anatomy

- from medulla oblongata to second lumbar vertebra
- cervical enlargement consists of nerves from the upper limbs
- lumbosacral enlargement consists of nerves from the lower limbs

Internal Spinal Cord Anatomy

- grey matter consisting of unmyelinated axons and glial cells, butterfly shape
- white matter consisting of myelinated axons

Anterior Horns

- grey matter in spinal cord
- contain cell bodies of somatic motor neurons which innervate skeletal muscle

Posterior Horns

- grey matter in spinal cord
- contain axons of sensory neurons
- cell bodies of interneurons

Lateral Horn

- grey matter in spinal cord
- found in T1-L2
- cell bodies of autonomic motor neurons
- innervate cardiac and smooth muscle and glands

Grey Commissure

- grey matter in spinal cord
- unmyelinated axons
- communication route between the right and left side

Spinal Nerves

- make up PNS
- connect the CNS to sensory receptors, muscles and glands

Meningeal Branch

- branch of spinal nerves
- returns through vertebral foramen to innervate meninges, vertebrae and ligaments

Rami Communications

- two branches in the spinal nerves that function within the autonomic nervous system

Dorsal Ramus

- branch of spinal nerves
- innervate deep muscles and skin of the back

Ventral Ramus

- branch of spinal nerves
- innervate superficial back muscles, lateral and ventral muscles and skins and muscles of upper and lower limbs
- do not go directly to body structures and form networks on both sides of the body

Cervical Plexus

- portion of anterior rami of the C1-C4 and part of C5
- positioned laterally
- head, neck, upper shoulders and chest

Phrenic Nerve

- C3-C5
- innervate the diaphragm

Brachial Plexus

- positioned lateral from C5-T1
- extends downward under the clavicle into axilla
- part of shoulders and all upper limbs
- 5 major nerves

Axillary Nerve

- from brachial plexus
- sensory from skin of shoulder
- motion to some shoulder muscles

Musculocutaneous Nerve

- from brachial plexus
- flexors of the arm

Radial Nerve

- from brachial plexus
- extensors of the arm and forearm

Median Nerve

- from brachial plexus
- anterior forearm and portion of the hand

Ulnar Nerve

- from brachial plexus
- anterior/medial forearm and majority of the hand

Lumbar Plexus

- side of anterior rami of L1-L4
- anterolateral abdominal walls, external genitals and parts of lower limbs
- 2 major nerves

Femoral Nerve

- from lumbar plexus
- anterior muscles of the thigh

Obturator Nerve

- from lumbar plexus
- medial (adductor) muscles of the thigh

Sacral Plexus

- immediately caudal to lumbar plexus
- formed by L4-S5
- lower back, pelvis, posterior thigh, parts of the foot
- one main nerve

Sciatic Nerves

- largest nerve extending the length of each leg
- irritation can cause crippling pain and discomfort, pinching of the nerve (sciatica), arthritic inflammation, bulging disk, vitamin deficiencies

Dermatomes

- area of skin supplied by a single spinal nerve (all but C1 innervate single portion)

Reflexes

- rapide involuntary reactions to a stimulus
- required to initiate a response
- few neurons must be involved and synaptic delay must be minimal
- occurs the same way everytime

Reflex Arc

1. stimulus
2. sensory neuron activated
3. processed in the CNS
4. motor neuron activated
5. response by effector

Telencephalon

- the anterior division of the forebrain consisting of the cerebrum

Diencephalon

- the posterior division of the forebrain consisting of the thalamus, epithalamus and hypothalamus

Mesencephalon

- midbrain

Metencephalon

- the part of the hindbrain that develops into the pons and the cerebellum

Myelencephalon

- the posterior part of the hindbrain that forms the medulla oblongata

Medulla Oblongata

- last portion of the brain before the spinal cord
- contains sensory and motor tracts to and from the brain
- controls heart rate and breathing
- vomiting, coughing and sneezing reflexes

Pons

- contains sensory and motor tracts that connect the brain and spinal cord (bridge)
- helps to regulate the breathing rate
- involved in sound localization

Cerebellum

- second largest part of the brain
- highly convoluted surfaced covered in folds
- coordinates and fine tunes skeletal muscle movement
- monitors position of joints and muscles

Midbrain

- between pons and diencephalon
- controls various sub or unconscious movement of the eye
- contains elements of the auditory pathway

Diencephalon

- contains the thalamus, epithalamus and hypothalamus
- surrounds the third ventricle

Thalamus

- paired oval masses of grey matter, each consisting of a dozen thalamic nuclei
- division of the diencephalon
- all sensory signals pass through here (excluding smell)

Hypothalamus

- division of the diencephalon
- involved in hormone production
- regulation of emotions, eating, drinking and body temperature

Epithalamus

- connects the limbic system to the rest of the brain
- division of the diencephalon
- main component is the pineal gland
- important for sleep regulation

Cerebrum

- location of conscious thought processes and the origin of intellectual functions
- formed from the telencephalon
- surface folds into elevated ridges

Gyri

- adjacent gyri are separated by shallow grooves (sulci) or deeper grooves (fissures)

Cerebral Hemispheres

- 2 components of the cerebrum
- divided by a longitudinal fissure extends along the midsagittal plane
- memory and consciousness can not be assigned to particular regions

Corpus Callosum

- main tract connecting the right and left cerebral hemispheres

Olfactory Nerve

- cranial nerve that carries impulses to the brain from the olfactory epithelium
- (I)
- sensory only
- only type of nervous tissue to regenerate
- anosmia is partial or total loss of smell

Optic Nerve

- (II) cranial nerve that carries impulses from the retina
- sensory only
- left and right optic nerves unite at optic chiasma
- information passes through thalamus on way to occipital lobe of cerebrum
- anopsia is visual defects

Oculomotor Nerve

- (III) cranial nerve that controls pupil size
- motor fibers to four extrinsic eye muscles and upper eyelid
- sensory fibers from proprioceptors
- damage causes upper eyelid droop, paralysis of eye muscles, double vision or difficulty focusing

Trochlear Nerve

- (IV) cranial nerve
- motor fibers to the fifth eye muscle
- sensory fibers from proprioceptors
- damage can cause paralysis of superior oblique muscle leading to visual issues

Trigeminal Nerve

- (V) cranial nerve
- motor fibers innervate muscles of mastication
- motor sensory fibers from the face
- divides into three branches

Ophthalmic Branch

- part of the trigeminal nerve
- motor fibers to tear gland
- sensory fibers from cornea, nose, forehead and anterior scalp

Maxillary Branch

- part of the trigeminal nerve
- sensory fibers from nasal mucosa, gums and cheek

Mandibular Branch

- part of the trigeminal nerve
- sensory fibers from the lower jaw and teeth and part of the tongue
- motor fibers to the temporalis, masseter and pterygoid muscles
- damage causes trigeminal neuralgia (inflammation of sensory components)