Nervous System

Development of the 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)