Muscle Review & Nervous System Intro (Week 6 – Ch. 14)

Muscle System Wrap-Up

• Hip & Thigh
  • \text{Tensor fasciae latae}: tenses IT band; hip \text{abduction (A\,B)}
  • \text{Sartorius}: hip flexion + lateral rotation; knee flexion ("tailor/cross-leg")
  • \text{Gracilis} + \text{Adductors (brevis,longus)}: hip \text{adduction (A\,D)}
  • Quadriceps femoris (knee extension; rectus femoris assists weak hip flexion):
  • Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius
• Leg (knee→ankle)
  • Anterior: Tibialis anterior (dorsiflex + inversion); Extensor digitorum longus (toe 2-5 extension); Extensor hallucis longus (hallux extension)
  • Lateral: Fibularis (peroneus) longus & brevis → foot eversion
  • Posterior (superficial): Gastrocnemius (knee flexion; plantar flexion) + Soleus → "triceps surae"
  • Posterior (deep): Tibialis posterior (inversion + plantar flexion); Flexor digitorum longus; Flexor hallucis longus (toe flexors)

Nervous System Overview

• Core functions: maintain homeostasis & coordinate activities
• Basic 3-step circuit: sensory input → integration (decision) → motor output

Structural Organization

• CNS (Brain + Spinal cord) ↔ PNS (nerves)
• PNS splits →
  1. Sensory / Afferent (→ CNS)
  2. Motor / Efferent (← CNS)
  • Somatic (skeletal m.)
  • Autonomic (smooth/cardiac m., glands)
    • Sympathetic (fight/flight) • Parasympathetic (rest/digest)

Neural Tissue Cells

Neurons

• Excitable, conduct & transmit signals, long-lived, \text{non-mitotic}, high metabolic demand

Neuroglia (support)

CNS (4):

• Astrocytes – regulate ECF; form blood-brain barrier
• Ependymal cells – ciliated lining of CNS cavities; move CSF
• Microglia – phagocytic immune analogs
• Oligodendrocytes – myelin in CNS
  PNS (2):
• Satellite cells – regulate ECF of ganglia somata
• Neurolemmocytes / Schwann cells – myelin in PNS

Neuron Anatomy

• Soma (nucleus, organelles; Nissl bodies = ribosome clumps; neurofibrils)
• Dendrites = receptive
• Axon (nerve fiber): axon hillock → axon → terminal branches → axon terminals (synaptic knobs/Boutons)
• Myelin sheath (interrupted by nodes of Ranvier/neurofibril nodes)

Neuron Classification

Structural (processes on soma):

• Unipolar (1) - Bipolar (2) - Multipolar (\ge 3)
  Functional:
• Sensory/Afferent (→ CNS; usually unipolar)
• Interneurons (inside CNS; multipolar)
• Motor/Efferent (← CNS; multipolar)

Myelin & Conduction

• Myelin = concentric layers of glial membrane → insulation & protection
• Larger axon diameter + myelination → faster conduction
  • Continuous conduction: unmyelinated (slow)
  • Saltatory conduction: jumps node-to-node (fast)

Synapses & Transmission

• Conduction = signal along membrane; Transmission = cell-to-cell at synapse
• Electrical synapse: gap junctions (ion flow)
• Chemical synapse (majority): neurotransmitter crosses synaptic cleft → excitatory or inhibitory
  • Example: Acetylcholine – always excitatory at neuromuscular junction; variable elsewhere
• Synapse types: Axodendritic (common), Axosomatic, Axoaxonic (rare)

Gray vs. White Matter & Nerves

• Gray matter = neuronal cell bodies
  • CNS: cortex (surface) + deeper nuclei
  • PNS: ganglia
• White matter = myelinated axons
  • CNS bundles = tracts
  • PNS bundles = nerves
    • Endoneurium (around fiber) • Perineurium (around fascicle) • Epineurium (around nerve)
• Nerve types: Sensory, Motor, Mixed