nervous system 1

 Radial Systems

Cnidarians, Echinoderms

Cnidarians

• Simplest animals w nervous system

• Nerve net:

  • Interconnected neurons, no central control organ

  • Impulses in both directions, spread through net

Echinoderms

• Technically bilateral but superficially radial as adults

• Nerve ring: central control structure

• Radial nerves

Bilateria

Platyhelminthes, Annelids & Arthropods, Vertebrates

Platyhelminthes

• Simplest clearly defined CNS

• Brain, eyespots at anterior

• Ladder-type nervous system – 2 longitudinal nerve cords, transverse nerves

Annelids & Arthropods:

• More complex brain

• Ganglia:

  • Segmentally arranged clusters of neurons

Vertebrates:

• Brain & spinal cord – central nervous system (CNS)

• Nerves & ganglia – peripheral nervous system (PNS)

Nervous System & Lifestyle

• Polyplacophora v.s cephalopod

Glial Cells

Cells of nervous system not directly involved in signal transmission

Examples

Astrocytes, Microglia, Ependymal cells

Astrocytes

• Blood-brain barrier, regulate extracellular fluids

• Microglia

• Protection & scavenging dead cells

Ependymal cells

• Line fluid-filled cavities

• Involved in production of cerebrospinal fluid

 Cells Involved in Myelination

• Oligodendrocytes in CNS

• Schwann cells in PNS

Embryonic Development

• Neural tube – single tube of tissue

• Anterior folds over brain – brain

• The rest – spinal cord

Brain

• Central control organ

• Gray matter outside, white matter inside

• Ventricles filled with cerebrospinal fluid

Parts of brain:

Cerebrum, Cerebellum, Thalamus, Hypothalamus, Brainstem

Cerebrum

Largest part, voluntary movement, learning, emotion, memory, perception

Cerebellum

• Back of brain, movement, balance, motor coordination

Thalamus

• Sensory input & routing

Hypothalamus

Regulates pituitary, hunger/thirst, sex, rage

Brainstem

• Midbrain, pons, medulla oblongata

• Routes sensory info, regulates basic life functions

 Spinal Cord

• Link between brain & rest of nervous system

• Dorsal neck/back, within spine

• White matter outside, gray matter inside

• Central canal filled with cerebrospinal fluid

spinal cord functions

• Functions:

  • Transmit impulses to/from brain

  • Reflex actions:

    • Rapid, involuntary response to stimulus

    • Ex: knee-jerk reflex

Peripheral Nervous System

Nervous tissue not part of CNS – sensory receptors, nerves

Sensory Receptors

• Detections of stimuli – visual, auditory, chemical, etc.

Nerves

• Bundles of axons

• Radiate from brain/spinal cord throughout body

2 Functional Components of PNS

• Afferent (sensory): sensory receptor to CNS

  • Receptors involved, not effectors

  • Efferent (motor): CNS to effectors

2 types of senses (Afferent (sensory))

• Visceral: not aware of – ex: blood pressure

• Somatic: are aware of – ex: vision

• Efferent (motor):

  • 2 components:

• Motor system:

  • Efferent neurons to skeletal muscles

  • Voluntary & reflexes

• Autonomic System:

  • Efferent neurons to glands, heart, smooth muscle

  • Not consciously controlled

  • 3 divisions:

    • Enteric – digestive tract, pancreas, gall bladder, more

    • Parasympathetic – “rest & digest”

    • Sympathetic – “fight or flight”

 Pathway of Signal

Stimulus – sensory receptor – afferent neuron – CNS – efferent neuron – motor or autonomic system – effector