Spinal Nerves

Serially homologous - one pair of nerves per

vertebra

(segment of mesoderm of each vertebra)

Named for vertebra with which the nerve is associated (S1, L3, C2, etc.)

-each has dorsal and ventral root

- the roots fuse to form the nerve

Dorsal root

Carries afferent nerves

Cell bodies grouped together just outside spinal

cord in dorsal root ganglion

Ventral root

Carries efferent nerves

Cell bodies in ganglia close to target organ

Also connect to sympathetic chain of ganglia along spinal cord

eading to perception

Cranial nerves

Encased in skull

Most are believed to be homologous with

spinal nerves

No distinct dorsal or ventral root

Numbered by present position, not homology

first few cranial nerves reside outside the skull (occipitospinal nerves in cyclostomes)

12 pairs in all tetrapods and crossopterygians

Living amphibians secondarily lost 2 pairs

Cranial Nerves

*Terminal nerve (0)

Believed to be remnant from lost visceral arch (support for Composite theory)

Sensory and motor fibers to/from olfactory epithelium & associated blood vessels

Present in all gnathostomes except birds

Olfactory nerve (I)

Sensory from olfactory sac

Olfactory Epithelium

 

Optic nerve (II)

Not really a nerve! Actually brain outgrowth

Integrates visual information from retinas

Optic Chiasma-where sensory information crosses over

No visual perception occurs at point of attachment to retina

 

Cranial Nerves

Oculomotor nerve (III)

Motor for some of the extrinsic eye muscles (superior rectus, medial rectus, inferior rectus, inferior oblique) and some visceral fibers to intrinsic eye muscles (iris, ciliary body)

Trochlear nerve (IV)

Motor nerve to superior oblique extrinsic eye muscle

Cranial Nerves

Trigeminal nerve (V)

Usually the largest of the cranial nerves

3 major branches

Deep ophthalmic (V1) - to lost first arch?

Most often fused with other two branches

Maxillary (V2) - upper jaw, roof of mouth and pharynx, sensory

etc.

Mandibular (V3) - lower jaw and floor or

mouth and pharynx, motor and sensory

-tongue tactile cues, lower teeth, chin skin, mastication muscles etc.

 

Cranial Nerves

Abducens (VI)

Motor nerve to lateral rectus

(another extrinsic eye muscle)

Facial (VII)

Sensory fibers from lateral line of head (fishes, amphibians) and taste buds

Motor fibers to hyoid arch

Primary motor nerves of face

Salivary glands, lacrimal glands

Some taste buds

Five major branches

Temporal

Zygomatic

Buccal

Mandibular

Cervical

Cranial Nerves

Auditory (VIII)

(acoustic, vestibulocochlear, or statoacoustic)

Sensory fibers from inner ear

hearing and balance

Glossopharyngeal (IX)

Sensory fibers from taste buds, first gill slit and adjacent pharyngeal lining, lateral line

Swallowing and gag reflex

Motor fibers to third branchial arch

Cranial Nerves

Vagus (X)

The "wanderer" - mouth, pharynx, much

of viscera

Only cranial nerve to extend beyond head and neck region

formed by fusion of C1, C2 and cranial

nerve

Most Parasympathetic efferents

Regulates heart rate

Breathing rate

Digestive system activity

Transmits sensory impulses from thoracic and abdominal viscera

Proprioreceptors of larynx, taste buds, motor nerves of larynx and pharynx

 

Cranial Nerves

 

Spinal accessory (XI)

Formed by branch of vagus + several

occipitospinal nerves

(dorsal and ventral roots)

Motor to derivatives of cucullaris (cleidomastoid, sternomastoid, trapezius) - all derivatives of branchiomeric musculature

Also portions with vagus to pharynx, larynx,

maybe heart

 

Hypoglossal (XII)

Motor nerve to hyoid and tongue muscles

Lateral Line Nerves

Vagus and Facial nerves

Anterior and Posterior

 

 

Evolution of Cranial Nerves

Derived from Pharyngeal Arches?

Dorsal and ventral roots of spinal nerves have fused or become lost

Some nerves are persisting dorsal roots

Sensory afferent (terminal, facial, glossopharyngeal, vagus, accessory nerves

Ventral roots -oculomotor, trochlear and abducens

 

 

 

Central Nervous System Protection (CNS)

  1. Encased in cartilage, bone, or

extensions of notochord

Composed of ectoderm (from neural tube)

 

2. Cerebral spinal fluid (CSF) reduces brain weight by 97%

CSF in ventricles of brain and central canal of spinal cord

 

3. CSF provides blood-brain barrier

 

 

4. Meninges

 

 

Meninges Function

 
  1. Cover and protect the CNS
  2. Protect blood vessels and enclose

    3. venous sinuses

  3. Contain cerebrospinal fluid

4. Form partitions within the skull

Fishes: Single Primitive meninx

Amphibians, Reptiles, and Birds

Two meninx:

dura mater-thick, mesodermally derived

secondary meninx forms beneath this layer

Mammals

Dura mater-thick white and leathery

Arachnoid-absorbs cerebrospinal fluid, provides blood vessels to brain, attaches pia mater

Pia mater -capillaries and delicate transparent connective tissue

 

 

Brain Divisions

1. Prosencephalon-forebrain

A. Telencephalon

Cerebrum

B. Diencephalon

Thalamus

Hypothalmus

Epithalamus

2. Mesencephalon-midbrain

No subdivisions (midbrain)

3. Rhombencephalon-hindbrain

D. Metencephalon

Brain stem

pons

Cerebellum

E. Myelencephalon

Posterior part of Brain stem

Medulla oblongata

Techniques for Determining Brain Function

Histological studies

Biochemical

Stereotaxic instruments (mapping)

Ablation

Function impairment

Determine pathway of neuron death

Anecdotal observations through human accidents, disease and/or surgery

Brain activity in living vertebrates

Magnetic resonance imaging (MRI)

Positron emission tomography (PET)

 

 

What we know:

Using an electrical wiring analogy is inadequate

No single part of the brain is exclusive to one function

Brains do more than transmit, reject, or store information

About 3 billion impulses reach up to 100 billion neurons every waking second

We don't know why vertebrates sleep-but they do.

We don't "only use 10% of our brains"

We haven't even determined basic anatomy of many vertebrates

Gross Brain morphology can be quite different, even between more closely related vertebrates

Echidna has gyri (ridge) and sulci (fissure)

Platypus does not

Dolphins have a larger and more convoluted cerebrum than humans

Functions of Brain Divisions

Cerebral hemispheres-(Telencephalon)-interprets sensory inputs, controls voluntary and skilled skeletal muscle activity, intellectual and emotional processing

Thalamus-(Diencephalon)-relays sensory impulses to cerebral cortex for interpretation, processes memory

Hypothalamus-(Diencephalon)-integrates autonomic nervous system, regulates body temperature, food intake, water balance, thirst, biological rhythms, and sex drive

Controls hormonal output from pituitary

Produces hormones (oxytocin, ADH)

Limbic system-(Telencephalon and Diencephalon)-mediates emotional response

Functions of Brain Divisions

Midbrain (Mesencephalon)-visual and auditory reflex centers, motor center

Brain stem (Rhombocephalon)

Pons-(metencephalon) Relays information from cerebrum to the cerebellum, controls respiratory rate and depth, 3 cranial nerves nuclei housed here (trigeminal, abducens, facial)

Cerebellum-(metencephalon)-processes proprioceptors and visual and equilibrium pathways. Provides "instructions" for maintaining posture, balance, coordinated skeletal muscle movements

Functions of Brain Divisions

Reticular Formation (metencephalon)-filters out repetitive stimuli, regulates skeletal and visceral muscle activity, regulates alertness

Medulla (oblongata)-(myelencephalon) transmits sensory impulses from skin and proprioceptors), controls heart rate, blood vessel diameter, respiratory rate, vomiting, coughing, relays sensory information to cerebellum

 

 

 

 

 

Comparative anatomy of BRAINS

Agnathans

Large olfactory lobes

Optic lobes evident (called tectum in Kardong)

Elasmobranchs and bony fishes

Olfactory lobes large

Optic lobes are prominant

Midbrain enlarged with 3-D perception

Amphibians

Cerebellum slightly more developed (sensory integration)

Reptiles

Olfactory slightly smaller than fish

Cerebrum enlarging

 

Birds

Olfactory tracts smaller than most others

Cerebral hemispheres enlarging and developing specialization of areas (hearing in OWLS)

Optic lobes markedly larger than reptiles

Cerebellum much larger

 

Mammals

Extensive neocortex

Optic lobes downsized (neocortex has taken over some of the functions)

 

Overall Trends in Brain evolution

Forebrain enlarges during vertebrate evolution

Cerebellum enlarges

Flexure causes medial portion of forebrain to roll under midbrain

Lateral areas of forebrain "grow" over the midbrain and hindbrain

Note increased cerebellum size with terrestriality

The above are just general trends - many differences occur between species

Spinal cord - specialized into gray matter and

white matter

Gray matter - cell bodies present

White matter - mostly axons, often myelinated

Quiz 12
  1. Name 3 of the 6 types of nervous system support cells (i.e. non-neurons in the nervous system). What is each of their respective functions.

    2.  

  2. What is the functional difference between an axon and a dendrite?

    3.  

  3. What is the difference between efferent neurons and afferent neurons within the Peripheral Nervous System (PNS)?
  4. What are three factors that affect the conducting speed of a neuron?
  5. Name the 12 cranial nerves in order. Indicate which one is not a true nerve.